Mine was a 2006 FST Classic and that was the first year. They were known to steer very hard but that was greatly improved with new spindles and other improvements over the next 2 years. I think they had that corrected by the 2008-2009 model year. I never did upgrade my spindles and I do ride trails fairly hard, but am slowing down some as I get older! I was maybe a little more tired at the end of a day, but I can't say it was noticeable to the point of being a problem. I'm guessing with the changes, it wouldn't be an issue. Whitedust is right on the heat vents to cool under the hood. Prior to installing those, I was blowing a belt every 1,000 miles due to the intense heat that is created by a turbo. Since I installed them, I never blew another belt.
If they were able to put a 4s in the new Rush platform, I would still be riding a 4s, but I had to have the new Rush once it came out with a 136" skid. I didn't want the IQ chassis again as I had put 12,000 miles on mine and didn't want the same thing. That engine was very reliable. Let me know if you have any other questions. Good luck!