Mark, you and I have very similar systems, right down to the problems experienced! I think you are being generous in writing things off due to “pilot error”. I am somewhat disappointed that I’ve got this MONSTER machine, with 6TB of storage on an external, fibre-channel G Speed drive, 6 gigs of RAM, and I still get these “hiccups”, weird stuttering video, and the frame dropping!
Mary Beth, the best I can do for you is to say I had the very same problem, and although it didn’t “solve” the problem, Command “R” to re-render the sequence, even if it’s been rendered, seemed to help.
I don’t know if I’ve got a compatibility issue somewhere or what, because as well as having the same problems described here my MacPro also “locks up” and becomes unresponsive, with the deliriously spinning rainbow forcing me to hard reboot.
You’ve got the right idea with the RT setting I think, I sort of go back and forth depending on what kind of mood I’m in. I find the frame dropping gets worse as I add effects and such. Command “R” can smarten it up.
Hang in there!