The cache is the most important difference between the two. The "classic" Athlons have 512k of L2 running at 1/2 or 1/3 the processor speed, while the T-Bird's have only 256k of L2, but running at FULL processor speed. Because the cache is running significantly faster, you get better processing performance out of the T-Birds. Definitely get a T-bird if you haven't already invested in a SlotA motherboard.