I know some sites selling pumps show tables of the GPH vs the head height. You don't mention what kind of filter you have and whether the pump will be driving through it. You want to filter about half to twice your pond volume per hour depending on fish load.

Shalom - When you look at the pump curves it will give you the gallons per hour per head so when you look for a pump you need to look way higher than 7500 and check the pump curve for the head it will be pumping against.

Look on ebay under pond pumps, you'll get a wide variety of pumps on one site which may help you do some comparisons and get pricing as well at one site. To date, I've bought most of my equipment off ebay and have been pleased. Many reptuable sellers are there, check their ratings. Where I bought my last pump, they were very helpfull, replaced a damaged coupler very quickly, no questions, just did it.

Most local pond shops will be limited on brands as manufacturers tend to control the number of distributors and also some expect certain sales volume to set up a shop as a distributor, etc.

Really, provide as much info as you can so forum members can help as each pond is unique and some may actually require 2 separate pump systems depending on how the pond is to be set up, what do you want to accomplish; KOi oriented, plant oriented, waterfall oriented - it all can make a bid difference.

Don't be afraid of oversizing pipe sizes, etc., you may well grown into ponding, think ahead - example had I moved my pond 3 feet more from the fence I could have had my swing on the high side of the pond looking down; yep, it's on the low side looking up - didn't think outside-the-box.

And, mabye the most important, you have to be patient, read whatever you can - the net is full of info.

Most ponders here have been through it - remember "most" pond shop's goal is to sell their products, many chemicals that try to get the pond "customer happy" very quickly. That's how they make their living, I'm a commissioned slaes person - no sale, no income - very simple. But the product must be worthwhile and many pond shops are very knowledgeable, but you need to do the reseasrch to know the difference.
Nothing happens quickly in a pond, naturally, and this is what is frustrating, many times, to ponders who pour in chemicals for instant results.

I've found the Devine definition of patience is ponding.

Sorry, more than enough ranting for one post.

I will share what I have done sucesfully with my pond. Maybe it will be of some help. I have a 11 x 16 pound with a set of falls with a rise of 12 ft high and a run of 30 ft.
I have a one HP 2 inch discharge Tusrumi pump (available on line)located in my skimmer. It goes to the biofalls on top of the hill and works very well. I have also used a 1/2 HP pump when the pomd was new 7 years ago. That worked fine too but I wanted more weter flow so I replaced it with the 1 hp.

I run my pump untill the ice starts to build to heavy on the falls. Then I pull the pump and store it in the basement till March.

I've had ponds for fifteen years and I have had excellent luck with PondMaster pumps. I have purchased online from Pondliner.com and Koi Village though I'm not sure he is still in business. Prices online were much better than local.

Can't help you with sizing, sorry.