Code benchmarking

Let's say I have 2 pieces of assembly code that do exactly the same thing. So is there any program out there that can benchmark and compare the two chunks of code, size- and speed-wise?

I suggest >>2's with millions of iterations, tested in a computer with normal loads. >>3 just got too hard to do, and there's a lot to consider. Pipelines, OoO, cache, multitasking and several sets of registers make it hard.