For a bigger guy, the 600 would tend run out of oomph. If you're like me, 175 or so geared up, then it might be enough, especially if they hit the 400lb mark they're talking about. I had a lot of fun on my old 600/144, but was more than ready when I stepped up to my 800. There's still a lot of fun to be had on a 600, but on the other hand, if you ride up high or are lucky enough to ride in deep stuff a lot, it's not like you have to ride hard to use the power of an 850.
I hear Cat was a real mess with inventory control not too long ago. Hopefully they've got it better figured out now - it's not a good time to be building sleds nobody wants. I do think the bubble is bursting, mostly because of interest rates. Most buyers are financing their machines, even though they're basically toys, and with interest rates skyrocketing, you're looking at around $50/mo more than a year ago. That may not sound terrible, but then consider that you're probably paying that much again in higher fuel prices (and maybe a lot more, especially if you drive a diesel to go ride, like me) just to do the same amount of riding as last year, and you're spending more money on just about everything else.
I think we're going to see some significant economic issues, and if so, the sled market is going to take a hit. In a roaring economy, I'd expect to see carbon fiber sleds and bigger engines, more turbos and such coming, but if things are rough, the value market will be where it's at. The price of new sleds is partly driving used sled prices, and will continue, but eventually you run out of good used inventory. Unless things get really bad, the market isn't going to disappear, but I don't expect any major rebound in the foreseeable future. So, whether I'm Cat, Doo, or Poo, I'd be putting more time and effort into bottom and middle markets - probably working towards a low-cost chassis and engine combination that's still got some fun factor. I know a lot of people want to see a 900 turbo slayer from Cat, but I have a hunch that if they want to weather the storm, they need to find a way to match a basic RMK/Summit for closer to $10k. It's definitely the wrong time to be gunning for the top of the market, in my opinion...