Leopard may be part of your issue, as it's more processor-intensive than its predecessors. It's not even officially supposed to run on less than an 867MHz G4, if that's any indication. Perhaps you could try installing Tiger on another drive/partition to see if that is your problem.
The iMac, while it has a slower processor and less VRAM, uses AGP video. Your Sawtooth uses a 66MHz PCI video card (if it has AGP, it's not a Sawtooth) which is markedly slower, regardless of the fact that the two chipsets are virtually identical (both are ATI RAGE 128-based chips).
If you're using uncompressed DV, then there's nothing for the G4 to do: it's really just a matter of taking the data from the disk, to memory, then to the display.
If it were MPEGs, there would be something for the AltiVec engine to decode, and the story would be different.
But yeah, I'd guess that Leopard is most of the problem.
The iMac, while it has a slower processor and less VRAM, uses AGP video. Your Sawtooth uses a 66MHz PCI video card (if it has AGP, it's not a Sawtooth) which is markedly slower, regardless of the fact that the two chipsets are virtually identical (both are ATI RAGE 128-based chips).
If you're using uncompressed DV, then there's nothing for the G4 to do: it's really just a matter of taking the data from the disk, to memory, then to the display.
If it were MPEGs, there would be something for the AltiVec engine to decode, and the story would be different.
But yeah, I'd guess that Leopard is most of the problem.