Alienware offer either the Intel SU7300 with 3MB cache or the SU4100 with 2MB cache with their m11x model. They both run at 1.3GHz, but are overclocked to get the performance required for current games (as well as being put with a decent graphics card).
My question is this: how much difference does the 1MB cache increase make, given that these 2 CPUs both run at the same speed and have the same number of cores (two), because it works out much cheaper to get the SU4100.
You wont see much different in gaming... which I assume is a priority based on waht your buying. You probly would see hardly any difference in normal computer usage either.
Defiantely save the money, no doubt.