Extra cache makes next to no difference at all with Athlon 64 processors. That's the main reason why AMD have stopped production of all A64/AX2 chips with more than 512K cache per core. The 4600's extra 200MHz will push it ahead of the 4400 for pretty much every task.
I actually did a little test of this recently using my own hardware. I set up two systems, one with an X2 4600 and one with a Sempron 64 3400+ overclocked to the same 2.4GHz as the X2.
You'd think the Sempron would get trashed given it has 256K L2 cache and single-channel memory against the X2's 512K and dual-channel. But the difference was basically nothing, below 5% for most things. In fact the Sempron actually gave slightly better 3D benchmarks than the X2, which I can only put down to the AGP port on the Sempron's VIA-based motherboaqd being a bit more efficient then the one on the X2's ULi based board.
