Which would be better... lower or higher voltage rating?

[EET]

So, I'm doing some looking for my dad, because he'd like to build a fairly up-to-date system in the future (current system is a 2800+ Athlon Sckt A). I figured for reference I'd pick a cpu, mobo, ram, etc. similar to mine 'cause I was kinda interested how prices have been affected... since I got almost everything from the 'Egg I thought it'd be easy (they don't have 90% of my stuff, figured that though). ANYway, I was looking at the AM2 4200+ (I have s939), and saw there were two different models offered, one @ 1.2-1.25v, and the other @ 1.3-1.35v. If he doesn't plan on doing any overclocking (which I'm not sure on yet), would it really matter which one I picked? I'm sure the 1.2v offering would run slightly cooler, but that's the only advantage I see outside of overclocking capabilities. Am I 180º off here?