RAM can be problematic if you don't have enough of it, it will cache data to the drive to compensate. Which basically means Disk I/O bottleneck times more than 2. If it's an option, you might consider breaking the files up into smaller files before editing them. Takes less RAM, loads faster, and stuff, but not for everyone.
I tend to use sox, but mainly because I like to script my edits. Perfect recall, 100% repeatable. Maybe not the best tool in all cases, but useful. You can combine many edits in one pass and prevent needless wear on your hard drive and wasted time on hardware I/O. And when you're talking GB's and hours in length a lot of extra time.
Quad core is pretty much the standard now. A faster dual core can be beneficial if you have and continue to use old software. But not always.