Is the i7 2.3 Ghz CPU significantly faster than the 2.2 one?
Even in CPU-intensive tasks, the difference is going to be more of the "noticeable in synthetic benchmarks" variety, rather than "I see it in the real world" variety. I'd save the money and put it first towards an SSD option, then more RAM.

Processor speed is almost flat these days, so minor bumps aren't worth the money.

My very aging MacPro got a new lease on life when I replaced the boot disk with an SSD earlier this year. There's nothing better for improving perceived responsiveness.