Choosing between cpus need help!!

I'd go for the P8600. The difference in speed isn't huge, and the P8600 is rated at 25W (vs 35W for the T series CPUs), which should give more battery life and cooler operation.

cjl pretty much hit the nail on the head. You may see a slight performance gain from the model with the higher cache, but its going to drop your battery life. If you're sitting on an average 6 cell battery, an upgrade to a 12 cell and you'll be in business with that T9500. I'd also be sure that it IS compatible with your laptop before buying. An exact model of the laptop and battery could be of some use.

From what I've seen the ms1651 should be compatible with the "T8100/T8300/T9300/T9500 CPU - 800Mhz FSB,1066 FSB" series CPUs in socket P pin out (keep in mind this information is not directly from MSI, but one of their 3rd party vendors; if I were you, I'd call MSI customer support and hear it from the horses mouth before forking out the cash for a new component).

FSB speed shouldn't be a main deciding factor here since you're only jumping 266MHz. The cache difference of 3MB will show a difference in compiling applications such as video editing or file conversion/compression. Gaming performance is affected mainly by the GPU.

MSI does have a 12 cell battery for this model if battery life is important to you.

With either choice, you're going to have a nice little system for portable gaming.