I am running 2.1.1 rooted, although you can use any version up to 2.3 (maybe 3.0, I think).
The reasons I am using 2.1.1 are:
2.1.1 is the most stable on JetDroid, and the current features work:
- Android Market
- Full 2D Acceleration and part 3D acceleration
Also on 2.1.1 you can easily root your phone, just plug it in with adb enabled and run z4root.
Using LiveWallpapersPicker.apk app i can also use live wallpapers.
Plus, I am making a HTC Sense theme for JetDroid
SetCPU only lets me set the CPU speed max to 800MHz btw.