"and i am looking at the opteron 165/170 vs 4200, with a small bit of overclocking, "
If your budget will handle it, look at the 170 or even a 175, as some MSI NF4 mainboards (my own K8N Neo-4F included) are somewhat allergic to FSB speeds of above 220-225 Mhz, regardless of HTT settings, mem ratios, or the newest mb BIOS. If your board happens to be one of them, the higher the starting cpu freq, the better...(ALthough at relatively high res gaming, the extra 200-400 Mhz cpu overclock is only good for 1-2 fps anyway, which is easily surpassed with even a 10 Mhz oc on gpu mem clock!)
(Good luck with it....some MSI boards do run 250-300 Mhz FSB with HTT4x,.. just not mine!)