Finally took my FS for a decent work out at the trails around Forrest (SE Australia). Wow. Very, very different to doing it on the cyclocross:
1) 2" knobbies...who knew they had so much grip?? I started out tentative around off-camber muddy corners where the CX would lose traction pretty soon (even with 35mm knobbies), but the thing just held on.
2) Disk brakes...jeez you can stop fast. Had to really learn to hold back on the front brake.
3) Low seat position: hit any small jump hard, and let the bike bounce back and forwards while you stay in the same position. So easy.
4) Front suspension: roll over almost log, ignore roots and rocks completely. (I previously stacked my CX on a very small log rollover just because I didn't lift the wheel hard enough)
5) Rear suspension: go over any drop-off without questioning it, smash your way through rock gardens or the bush...
6) Small wheels: weave through trees a lot quicker.
On technical singletrack, they're both a lot of fun. But the cx is fun the way beating your dad at chess is fun, whereas the fs is fun the way getting smashed with your mates is fun...
I know I'm preaching to the converted here, but, wheee...you can really go fast When I get a GPS, I'm really looking forward to taking them both for a spin around the same tracks, to put some numbers on it.
Next thing to figure out: how and when to use the rear brake. On the CX (cantis), most corners require decent force on both brakes, but I can see there is a lot more subtlety when you have so much power and grip.
I probably still have both shocks set too soft, but I'm still enjoying the novelty, and I don't think I bottomed out either one.
Only thing the FS sucks for is climbing on gravel roads. Oh, and the Sram SX4 shifters are poo, but what do you expect for the price I paid...