I just paid 11,500 for my Apex GT...10 grand for an 07 RTX with that many miles is a pretty good deal. You don't really feel the weight of these sleds, it will feel alot lighter when driving compared to your old SRX, remember there is lots of technology in these. I personal thought that a 800 REV and my Apex feel the same when riding them, only time you notice the weight is when lifting them around. As for the power, i have raced 3 ski-doo 800's already and they took me out of the hole cuz i don't run studs, but once i hooked up i was gone, i pass them with ease, and much more faster on top end, lots of torque. The motor is very strong, and will last forever. Burn no oil, there is no way to compare a four-stroke and thoses piston popers. That sure is a good deal on both sleds though, its a tuff decision. But the RTX has way better suspension and shocks. Remember, these sleds are not the same price when you buy them new, the RTX is another $1,700 bucks, so if you take that off the 3,000 bucks you are paying for the difference, you are getting a sled with 2,500 less kilometers, 1 year newer, updated handle bars, mudflap, and chaincase for $1,300 bucks. So i would go with the RTX. Plus you have a sled that is made for the ruff stuff if you just want to hammer down some days.
A phazer is a light sled, but they only have 80HP and go 90MPH, the Nytro's are nice sleds, but they don't have as much top end as the Apex and will cost with tax over $16,000 up here in Canada.