I would do Cat unless you are willing to travel farther. It will be low water by then and the water will be swimable warm! Perhaps you can get a raft for that, it helps carry the beer.
incidentally a few of us did JarB last year, and you all should put that one on the list! We will call 1500 a medium flow, allow for 4.5 days total from Colorado if you have a 20 year old to drive all night. That gets you 3 nights on the river, one day being like a 30 miler.
I've never boated before, but I have posted a lot on Mountain Buzz!