Ovenmitt and Stoneburner are right. I'm running my RAM at 258 with a 1:1 ratio right now (DDR516). If I ran a 5:4 ratio, my performance would suffer quite a bit, because of the lack of an on-die memory controller, and that's why I previously purchased overclockable RAM. The A64s (and opterons), however, don't suffer much from running a memory divider, so I ordered 2 GB of somewhat value RAM and plan on running a divider.
Lark888, running at 302HTT 1:1 would yield better performance than running at 3:2, but the cost does not justify the performance gain IMO.
For example, if you have $500 to blow on 2 GB of RAM and a video card, it wouldn't make sense to buy some uber-overclockable RAM and a 6800GS, rather than value RAM and a 7800GT. However, if you're running two 7800GTX 512MB cards in SLI, then by all means drop $300+ into your RAM to see some performance gains.