Unless you're using Avid or something, you shouldn't be locked into using Quicktime to edit. You're on the right track, though - getting the footage away from RM is a good idea. You'd be best off skipping it and getting the Xvids or rip the mpeg2 from the DVDs yourself though.
If that's absolutely not an option, look up Huffyuv. Huffyuv isn't a program, it's a codec (contained in AVI). It's extremely fast and the output is 99% the same as what you throw in. It's basically a lossless frame compression. Convert to Huffyuv using something like River Past Cleaner (or even Virtualdub), edit the Huffyuv formatted footage in whatever editing program you like.