Geebus, some of you are on some of the funky crack rock.
Buy the 2.8Ghz with 1GB of RAM. Then upgrade your RAM elsewhere (it's much cheaper). Processors are insanely harder to upgrade (if at all possible) and more expensive. With RAM, you go buy a couple of modules.
I also could be mistaken, but I don't think a lot of you understand how computers work. The processor actually does the work, but RAM is a very fast type of memory where processes can be stored or executed by the processor. Cache is the fastest (and most expensive) type and will speed up the processor the most. If you want proof, look up "Intel Celeron." It's in the dictionary under "POS."
The thing is all of this is kinda moot depending on any given system or software. Every computer has a bottleneck at some point, and you basically want to make your bottleneck as far away from your everyday stuff as possible. I have 2 GB of RAM and I have never seen my iStat meter say it's completely used up, no matter what I do. But when I run HandBrake, it will suck up all the CPU it can. If I try to watch a video doing that, it sometimes gets choppy. HandBrake will do this no matter what, but the more CPU you have, the better.
Getting to the point, always get as much CPU as you can afford. RAM can come later.