I'm using a 17" TFT with my CV64/3D + scandoubler combo, and haven't had any problems yet. The autoswitching works really well.
I'm running a CSMK2 + SCSI, CV64/3D + scandoubler and X-Surf 2 in an A4000D case, and haven't gotten any problems with heat or stability problems. Be aware of the PPC CPU though, it is very fragile, and gets very hot, so your need for cooling is higher than my needs.
