Do you have the deluxe or the premium or the plain? The deluxe which I have and the plain SLI has the 240-245 1T problem. Which means you cant run ram over that speed, 242 in my case with a 1T command rate it will BSOD and crash regardless what type of ram or settings. The performance penalty for running a 2T command rate makes it a bad move to run 250 and over with 2T unless you can get over 300 2T then its marginally faster than 220-230 1T. The premium model doesn't have this problem.
That VX ram really operates best with over 3 volts. But with 3.0 volts it should run 2-2-2-7 up to 230-240 with no problems, maybe even 1.5-2-2-7 (seven bench's better than 5 or 6 or 8). It will probably do 2.5-3-3-7 up to about 290mhz
If you have the plain or deluxe mobo, this ram is not a good match I would RMA it for some TCCD or TCC5 or even the value ram, or swap mobos for the DFI ultra series. High ramspeed on A64's is really only good for synthetic benchmarks. Unless your main purpose is competive benchmarking high ram speed won't make hardly any difference in gaming and normal day to day apps.