memory comparison brands

It isn't just about brand, each brand makes both high-quality and low-quality parts. Personally I hate Corsair as they use high quality chips for one revision to draw attention to their products then switch to really cheap chips as soon as they start selling well. Crucial has some good ram, but I have had bad luck with Ballistix dying on me(at Crucial specified 2.2v, which is a bit higher then most). G-Skill makes good budget and high-end products, as does Mushkin. OCZ makes some good stuff and some stuff that can't overclock worth jack(DDR2-800 Platinum Revision 2 for example, my friend couldn't get that over about 830MHz).

good points.... how do i tell what is qualityparts though? as gravemind1 23 mentioned

Well, if you find two kits with the same speed and timings, but one needs less voltage, it is likely based on better chips, because voltage is used to help boost stability when chips aren't able to handle running at certain speeds at the default 1.8v

In the past the quality made more of a difference, with Micron D9G** chips being much more overclockable then ProMOS, Elpida and other chips makers chips. At this point, the cheaper manufacturers have had the time to mature their process enough that overclocking differences aren't as big any more. That and Micron no longer makes D9G** chips and they can't be used in 2GB sticks anyway.

If you get DDR2-800 that can run that speed at 1.8v you should be fine for running at any stock or mild to moderate overclock(depending on CPU).

It is likely beneficial because it provides higher memory speeds and bandwidth, and from what I've read on the AM2 platform(my memory is a bit fuzzy as this was closer to its release), it seems to gain performance with higher memory speeds, unlike Intel's current line-up, where the increase in memory speed doesn't do much at all for the performance.