For starters, the Q4000 is the lamest CUDA GPU you can install.
Is there a point (removing nodes) where your playback/render speeds start improving?
What is the codec — ProRes, H264, HDV, DVC, uncompressed 10-bit… etc.? These can affect CPU pass-through and bitrate to and from the source drive.
And, of course, the sustained bit transfer rate from the source drive… A Rugged LaCie FireWire connection is not really ideal, for example.
jPo
“I always pass on free advice — its never of any use to me” Oscar Wilde.