3470 is about 11-12% Faster than the 2400: http://cpu.userbenchmark.com/Compare/Intel-Core-i5-2400-vs-Intel-Core-i5-3470/803vs2771
with the 2500, the 3470 only 2-3% Better: http://cpu.userbenchmark.com/Compare/Intel-Core-i5-2500-vs-Intel-Core-i5-3470/m517vs2771
Besides the Performance, the 3470...