hello,
for a programmer how much does core i5 430m(2.26-253GHz) differs from core i5 450m(2.4-2.66GHz)?
It differs as you can see i5430 is less powerful than i5 450m. You can see the difference in this links Intel® Core & Intel® Core.
I would say that the real difference is how you use it - if you want to program in assembler or something, there are probably some differences, but otherwise it’s just the raw MHz difference.