After having issues with high temperature of MBP Unibody in high CPU usage over period of time, I think it's best to stick with 2.53. The battery life of 5 hours are not happening as well, I got only 2-3 hours for a month old MBP, having higher CPU will only shorten the battery life.
I personally felt regret to have paid over 400$ difference to upgrade form 2.4" to 2.53" base model, but I am paying for GPU memory which is not upgradeable. The meagre upgrade on CPU and HDD is not worth the money.
However, the 17" is only 200$ different from 15.4" 2.53Ghz. That's a worthy upgrade to pay for...