I've never done an apples-to-apples test of those two particular models, but here are some general factors that could make a difference:
1) Details of the video subsystems and CPU type and speed. The 604 is not a huge leap beyond the 603ev, as it turns out.
2) As you mentioned, the speed of the hard drives can make a difference. More important, capture to a defragged partition (preferably freshly wiped), or you can have spectacularly lousy results.
3) The OS: 8.6 is generally better than 8.1 for vidcap, for example.
4) Turn off networking and disable all other apps/processes that may compete with capture. Don't even move the mouse during capture.
5) Turn off VM. Failure to do so is a common source of bad sync.
6) Other oddball tidbits: With some model/OS combinations, you even have to move the capture window to a particular corner of the screen (e.g., lower right) to improve capture performance.
1) Details of the video subsystems and CPU type and speed. The 604 is not a huge leap beyond the 603ev, as it turns out.
2) As you mentioned, the speed of the hard drives can make a difference. More important, capture to a defragged partition (preferably freshly wiped), or you can have spectacularly lousy results.
3) The OS: 8.6 is generally better than 8.1 for vidcap, for example.
4) Turn off networking and disable all other apps/processes that may compete with capture. Don't even move the mouse during capture.
5) Turn off VM. Failure to do so is a common source of bad sync.
6) Other oddball tidbits: With some model/OS combinations, you even have to move the capture window to a particular corner of the screen (e.g., lower right) to improve capture performance.