I need to buy 8GB DDR3 for my new motherboard (MSI 990FXA-GD80) and was wondering if there's any significant benefit in terms of heat or power consumption with 1.65v vs 1.5v vs 1.35v?

I've got to get low-profile RAM as rather stupidly the 990FXA-GD80 forces you to use slots 1 (nearest the CPU) and 3 for dual channel operation, and the Corsair Vengeance I bought last month won't fit in slot 1 under the fan on my TRUE rev.C.

The 1.35v RAM I saw is the Mushkin Blackline at £36 http://www.aria.co.uk/SuperSpecials/Oth ... perSpecial

The 1.65v Corsair XMS3 is a bit cheaper (£30) http://www.scan.co.uk/products/8gb-(2x4gb)-corsair-ddr3-xms3-pc3-12800-(1600)-non-ecc-unbuffered-cas-9-9-9-27-165v

The 1.5v Corsair XMS3 (and other 1.5v) is the most expensive at £41.76 http://www.scan.co.uk/products/8gb-(2x4gb)-corsair-ddr3-xms3-pc3-12800-(1600)-non-ecc-unbuffered-cas-9-9-9-24-15v

I've seen some 1.5v Crucial Rendition, which would be the cheapest at £26 for 8GB, but I think I'd prefer something with some sort of cover/heat spreader http://www.ebuyer.com/291000-crucial-4g ... 1264ba1339

I realise the Rendition is 1333Mhz whilst the rest are 1600Mhz, but the tests I've seen don't seem to show much benefit and there's no guarantee anything would run at 1600Mhz with a Phenom II X4 (which only officially supports 1333Mhz). If I recall correctly, running 1333Mhz with tighter timings (i.e. tighter than 9-9-9-24) gives more of a boost, but of course I don't know if that's going to work with the Rendition either.

Last year THG stated that a set of low power Kingston DDR3s (either 1,25 or 1,35V) would boost system efficiency by a small margin (probably around 2% on average), with reference to 1,5V RAM, with a lower power consumption of about 0,5-1,5W at idle, up to 4-6W under heaviest load (average was 1-2W IIRC).

Several sources also report that Kingston LoVo DDR3s overclock better than 1,5/1,65V RAM, but then you'll lost the power savings advantage.

So, is there any benefit? Definitely yes. Is it noticeable? YMMV: it will be just with very low power systems IMO, so it will be not dealing with an high end Phenom II (maybe furtherly mated with an high end GPU).

Eventually, if your primary concern is savings on total expenses, you would do better going with standard voltage DDR3, IMVHO.
That said if you trust any how what THG said (personally I don't trust THG so much, but it does lots of articles and it's often one of the very few sources available about several arguments).

Thanks, that helps a lot.

As it's going with a Phenom II X4 955 and a HD6950, I might as well just get whatever's cheapest (including shipping) then, which excluding the Rendition which I'm not keen on, is probably going to be the 1.65v Corsair XMS3, but there's not much in it either way, so maybe I'll get the 1.35v Mushkin but I need to check which is likely to give the best speeds with my board/CPU.