The number one criteria that makes or breaks the CPU calculations/sec is actually the Front Speed Bus (FSB). You want to get the fastest one available and I believe for laptops the fastest is currently the 800 MHz FSB CPUs:
T9300 2.5GHz/800Mhz FSB, 6MB L2 Cache
T9500 2.6GHz/800Mhz FSB, 6MB...