Looking back at the T2130 1.86Ghz vs T5500 1.66Ghz suggestion .. I'm pretty sure this would have been going backward in terms of performance.
Or maybe not. Pentium Dual-Core Mobile T2130
scored 812 points on the Passmark CPU benchmark test. And Core 2 Duo Mobile T5500
scored 925. That's about 14% in favor of the T5550, quite a bit more than I expected.
But it's a very small increase in performance if you're talking about buying a new CPU and going through the trouble of installing it.
Core2 Duo T7600 @ 2.33GHz scored 1341. Or about 65%...