I doubt you'll find a stronger mower engine than Kawasaki. I have a Snapper mulcher that bags well but if I bagged often I'd go for one of their HiVac models. Mine is the CRP2160KWV but the P2160KWV might be better or your needs. The CP2160KWV is the same mower but with steel wheels which I've found are worth the difference.

Here is a link that might be useful: Snapper HiVac

Well, I have a Kee lawnmower with a Briggs Intek 5.5 horizontal shaft belt driving the deck. The mower has circular discharge of grass rather than a chute, and its like a bushhog. I mean, I can cut down 4 foot tall ditch weeds with it without it bogging, yet it leaves a beautiful cut in short grass as well. I used to have a Craftsman with a 6hp Tecumseh, and the Kee feels like it has 10x the blade torque of that mower.

Only problem is, I dont know if the Kee mowers have bagging/vacuum attachments. You got money to spend and really want something bad@ss? Get a Scag walkbehind with a Velocity deck. If its anything like the 48" Velocity on a Tiger Cub, you wont be disappointed.

Only downside is

I've owned a Toro Super Recycler for 5 years and find that it both bags and mulches exceptionally well. New models are comparable with mine. It will fill the bag with damp heavy grass and not bog down. Controls on the Super Recycler series are well designed and easy to use.

BTW, when picking among lawn mowers from major manufacturers (Toro, Honda, Snapper, Lawnboy) my suggestion would be to focus on how well the controls work and it's mowing ability. You can safely assume that any of the makers will provide an engine with more than enougn power to do the job.

IMO the Kee (later known as Trailmate) 3-wheel mower, made in Sarasota Fl, and equipped with a B&S 6 HP commercial engine and a cast aluminum deck is the best self propelled walk behind mower ever made, but sadly they are no longer manufactured and some parts are not available. That said, if you ever find one for sale, buy it immediately. A machine shop can make any part needed to put it in first class shape. I have used one for 22 years on five properties weekly. Replaced one tire, and belts every few years. Recently had to have a new transverse pulley assembly made by a machine shop(80$). That's it in 22 years! A beautifully designed mower, extremely easy to maintain and tough as nails, with zero turning radius. Mows beautifully, extremely easy to push around and maneuver, can mulch but does not bag. The new cost of these mowers equipped as stated was about $850, 22 years ago.

A Toro Super Recycler or Super Bagger should get the job done. It will vacuum and bag large a large volume of moist grass with ease. Please note that deck and bag design are primary determinants of how well the mower will process cut grass. It is safe to assume that the major lawn mower makers like Toro, Honda and Snapper will select the appropriate engine for their machines. The engine brand name is irrelevant to making a choice between mower models.

I mow 5 acres once a week with a Kubota Diesel 60" z turn but needed something to use in the ditches and around the tight spots that big mowers can't get into. Since I use a 5 year old Trailmate/Kee at work (High School Bldg & Grds Mgr. my first choice was a Kee. Went to the local mower shop where we purchased the one for the school and discovered it was no longer available commercially but one of the clerks mentioned she had seen one for sale on Craigs List. Wasted no time getting it in my garage, $300 used, (new cost for our school's mower was $900 in 2005). These things are bullet proof, you can't bog them down. They won't win a beauty contest but you CAN NOT KILL THEM. The design is simplistic but it does exactly what it was born to do. Cut The Grass. The belt design saves your engine from damage due to sudden stopage, stumps, rocks... Also the engine does not have to run at such a high RPM to do the job, I guess from the belt pully design, the blade tip speed is still fast enough to get it done and not bog down. By the way, bagging is a big no no. You are throwing away free fertilizer. Think About It. Bagging is a pain any way, having to stop every 5 minutes and dumping the bag and all.

My next choice on the list had I not been able to find a used Kee would have been a new SARLO, also made in South Florida where they cut grass practically 12 months out of the year. They also have a Diesel push mower that you can Will to your Great Grand Kids. 1 Gallon of Diesel per 8 hours mowing. The Flordia State Corrections Dept. loves them. They are goober proof and last forever. They have the figures to back them up.

I would not waste my time and my money for the "Throw-A-Way" mowers available at the local big box stores. How long due you really expect them to last any way? From the frame to the over worked engine. Three years and it's in the dumpster.

I cast another vote for the Toro Super Recycler. It really plows through the heavy grass and starts on the first pull.

Trying to bag wet grass will tax most any mower!
You simply have to mow more often. Filling the rear of the bag is difficult with long grass.

When my grass "gets away from me", I mow with the rear discharge and wait a few hours (longer is better up to a point). That allows the cut grass blades to dry some. I then go back and bag. The bag fills MUCH fuller since you have lighter and shorter (since they are cut again) grass blades to "throw" into the bag.
Sometimes it's actually quicker to do it that way instead of trying to dump 1/3 bag and unclog a deck every couple minutes.
SHARP blades also help as does a CLEAN air filter. The engine is "gulping maximum air when it's bogging. Any restriction hurts power.

Once a week cutting of grass of your type is the norm . I would simply purchase a Brand Name side discharge mulching mower and leave it at that. If you got caught between rain storms you could side discharge and later mulch when the grass had dried somewhat . Hell with bagging . I,am over 60 with approx 2 acres of grass to cut and even with a recent hip replacement have kept up with routine cutting . I only used a bagging (Lawnboy) once and never would go through bagging again lol . I have contemplated a rider , but not quite yet . Ensure at least 5.5 HP for any mulching application and keep your blades sharp . All the Best Bro !

I don't see how much area you mow. That sure makes a difference on what to buy. I bought a WAW34 by Gravely at the begiining of mowing season last year. It has a 10.5 B&S and cuts a 34" path very well. Although this is considered their "homeowner" line of mower, I don't see it wearing out anytime soon. I'm not sure if they sell a bagger, but this one came w/o it and is a side discharge. Regardless of how high the grass, this thing seldom, if ever, revved up. I keep up 3 acres and follow "The Beast" for exercise at least twice a week. Not sure I'd spend the $1400 for a new walk behind, but this one is great and was half price from a guy who had not used it more than 15 hours. It is a workout to manuever, so again, it depends on how much grass you are mowing.