Is my memory running at DDR2 800? AM2 Divider Problem!

Ok, Long story short... My ram (Corsair XMS2 Pc2-6400 5-5-5-15) is not approved by Corsair for my mobo (ASRock ALiveNF6G-DVI). All their approved models are Pc2-5300 or lower. My motherboard will not auto detect or by any other timings run my memory at 400 according to Cpu-Z. Comes up at best as Cpu/5 at 320. By overclocking my cpu (sempron 3000+) to 250 and tightning up the timings 4-4-4-13, Cpu-Z says its running at 400 and Cpu/5. That puts my Cpu at the same clock as the Anthlon 64X2 4000+/3800+ cpus which should run ddr2 800 just fine. Obviously mine won't preform the same due to lower cache and 1 core. So in reality have I just done the best I can with my situation and made my components work or is there something I'm overlooking? The reason why this is the short story is it would take 10 times more to explain WHY I have these components. I'll be doing some 3dmark and post the differences in scores if any.

Have you tried increasing the DIMM voltage above the standard 1.8V? Most RAM sold as DDR2-800 needs higher-than standard voltage to achieve that speed.