8 tracks of a drumset processed with about 2 plugins per track, sent to a buss that has a single stereo plugin.
When I hit the solo on the buss, the buss solos out fine, but when I hit the solo button to turn it off there's a huge spike and the system sputters continuosly for about 5-10 seconds.
When I hit solo or mute (hey, it DOES usually seem to be when I'm doing it to a buss...hmmm), I haven't noticed in particular the CPU spike, but I have noticed Vegas just locking up (going non-responsive). It doesn't do it all the time, but does seem to be related to how long the session's been running (i.e., the longer the session's been running, the more likely that it's going to lock up the next time I mute/solo a buss). It has done this in Vegas 4 and 5. I do have UAD-1 plugs, and I'm generally using one or more of them.