Actually, the FST is a great sled and only suffers because, Polaris did such a poor job of getting that sled ready for prime time. Once the fixes got done, it was a good all around machine.
Unlike the early CATs, there was zero turbo lag. Mileage was right around 15 give or take depending upon off trail or trail work.
Polaris designed the switchback sleds with 144 track which is about minimum in my opinion for an off trail unit. The rails are tipped up so that on harder surfaces, it acted more like a 130 or 136 which prevented some of the push longer track sleds exhibit in the corners on trail use.
I had a pair of these and still own one.
Polaris skis' suck...plain and simple. If you get one, figure on changing out the skis, and the spindles as they had wrong configurations in the early models. Also the 1.25 inch track is just short of bad for off trail use. I put a 2 inch track on there and geared the sled down (which was another issue with the early versions if you intend to use it off trail at all) and the sled wakes up lets the belts live a longer life and still goes like a rocket-ship with better mileage, while probably suffering on top end....so you won't be able to go 118 mph. (I have never opened the sled up to see.....)
The sled is about 85 pounds heavier than the 600 which also had marginal power for off trail. While the sled is heavy... the power is key to staying out of trouble so it is a mixed bag....and despite what others say who, no doubt have never taken one out and put it thru it's paces, ALL sleds are too heavy when you stick them. Wider skis are key to keeping these beasts noses up, and I have had mine in 4 feet of untracked powder and she bulldozes along just fine. The gauges are best in the industry with thumb controls on the bars where they belong rather than having to take your hand off to push a button while the sled is bouncing and carving up on the unit itself. Hand warms work great, brakes superb, suspension puts most others to shame....at least on the switcher. Unlike the yamaha that has exhaust noise, the Polaris is quiet exiting into the snow where most sleds put exhaust.
It has NEVER overheated....not even close, and most guys changed out the heavy muffler and took out the radiator bringing the weight down almost to 2 stroke range.
Unfortunately after 3 years, Polaris shortened the sled to 136 (the same year that Yamaha extended theirs out to 144) and coupled the suspension which took the best attributes of the off trailer away. Look for a 2006-8 model if you want a sled that does far better off trail.
Personally if you are going to go turbo, I would look at a 2010 or later model TZ-1, get the factory extension kit and longer lug track, extend the factory 144 to the 151, put some wider skis on the front and find out what crazy fast is....I owned one of those too. It ran smoother, got the same gas mileage as the FST and even tho it was way more machine than the FST, it was put together much better. (You can find one of these in the EXT version which comes stock with 1.3 inch and 144 track.)
While there is no doubt that lighter and powerful 2 stroke sleds have the advantage in pure off trail work, a skilled off trail rider on a turbo can go anywhere the others care to go, which is why lots of guys who could care less what the costs are, use them out west in 10 feet of snow. Power is the ultimate savior where a wimpy motor can't do it.
Still the early years switchback is a good cheap entry into turbo world, and a great balance of power to sled, if you put the above mods into it, you will not be able to wipe the smile off your face when you get into the powder to play with it. Others will disagree with me, but I would never ever use a sled with less than 2 inch lugs unless I never intended to go off trail at all. The difference is night and day off trail, and the on trail use is still very respectable in all but ice conditions....where studs will be the only moving machinery.
Warning tho....once you go turbo, there is NO going back...unless you turn 85...and need crutches.
