Actually, if anything, you will be loosing out with a 170. ALL THE OPTERON 165's I've seen clock better than their 170 brethren. Might just be more people have them, but most/if not all are getting CCBBE's with the 165...and there are a lot of people with crappy 170 stepping's. See my sig! Picked it up like 4 weeks ago, from mwave.com. I guess I hang out at dfi-street a lot and most people there are running 165's because...uh they have THE BEST S939 motherboards built and could give a darn what mulit their chip has. As long as their ram can keep up, anyway.
The key here is your ram, if anything. Do you KNOW how high those sticks can go? Those Mushkin LII's should be able to hit DDR500-you are going to need that ability especially with the 165 because some of them don't like the dividers under 166 (i.e 150 and lower just don't work...luckily 150 is working for me!).
You better have that Antec psu ready with whichever dual core Opteron you pick up. And ALL the bios's are award v6. A date code would be much better! Personally, I like (as does happy/angry_games) the 7-04-2BTA bios.