I would have to say the first one as it provides more potential than the second one, which is essentially maxed out. You can upgrade the RAM on the first one for dirt cheap, making it a faster computer for slightly more than $2200
Bingo.
Having said that, when I was building gaming rigs in the later 1990's and early 20's, anyone doing that always knew that getting the very fastest processors was a complete waste of money, and the real trick was RAM and a decent gfx card. The same still applies today, although if you don't intend to game, a slightly faster CPU is peferable to a killer GPU.
In terms of real world performance, the 3ghz model will five you about 3 or 4% more speed.
Now the really exciting thing to look for is Nehalem, at the end of this year. at the same clock speed, with the same number of cores, Nehalem has been shown to be more than 120% faster than a Quad Core Penryn. Nehalem will boast 8 cores and 16 threads, possibly making it anything up to 200% faster, clock for clock.
Nehalem could be one of the biggest jumps in CPU performance from one generation to the next, ever.
So... rather than eeking out 3% now, for an extra $300 or whatever, I'd either stick with what you have and get one of these bad boys, or get the one with more memory.