Retrospect and FW 800 vs FW 400 - worth it?

[bunner bob]

I use Retrospect to back up (with compression) to an external LaCie drive with both FW 400 and FW 800 interfaces. Right now I'm using a long-ish (15') FW 400 cable since I keep my backup drive secured away from my desk. When I'm doing a full backup of 300+ gigs it takes quite a while. I was wondering whether using the faster FW 800 interface would speed things up, or if the weak link is something other than the data transfer. Since Retrospect must scan, copy and log everything, and compress it in software (this is a G5 dual-core 2.3 gHz), my thinking is that might be the bottleneck, so going to FW 800 wouldn't make a difference. I'm pretty sure doing a drag-copy across FW 400 is a lot faster than doing a Retrospect copy, which would point to the processing as the bottleneck.

Any thoughts - before I buy an unnecessary 15' FW 800 cable?

- Bob