I wouldn't disagree with a full PR lawn, as PR can be just as dark and thick as KBG. It germinates and establishes very quickly, your first mowing will probably be in about 3 weeks. On the downside, it's a bunch-type grass with no real spreading ability, so you will probably have to overseed at some point down the road. It can be prone to certain diseases, but most cool season grasses have their issues in that respect. It is pretty wear tolerant too, so can take some traffic with no problem. It can also be mowed low if you prefer that, although this can decrease root growth and increase water usage. It can die out in times of drought, as it doesn't have an extensive dormancy.
I would not do a KBG/PR mix in your showcase area. PR grows faster and more upright than KBG, and unless you mow often, it might have a ragged look at times. I would stick with a blend of elite KBG cultivars in that area. Personally I would do both areas in full KBG if I could, but that's my preference. KBG takes a longer time to get established, and doesn't really hit its full stride until it's at least a year old, and it gets even better as it matures. Most cultivars are pretty wear tolerant, most baseball parks above the transition zone use KBG, and I think we can all agree that Yankee stadium would make a pretty nice lawn.

I see you are in Z6B which tells me you likely get some pretty hot summers and rye grass does not stand up to heat very good without quite a bit of water.