centrino 2 is the platform, not the cpu. the cpu in the fw11s is a p8400 c2d. the fw21z has a t9400 but i dont personally think its much of an advantage over the p8400. the screen is great but @ 16" maybe text would be a little too small.
the fw21m has a bluray writer and a 1600x900 screen so that'd be the one i choose, unless you can find a cheaper 11s as they are essentially the same laptop anyway (p8600 in the 21m, i think thats the only difference)