GTX460 replacement thinking

For a little over a year, I've been operating two hosts with GTX460 graphics cards. Running a factory overclocked card, with quite capable host CPUs heavily underloaded with CPU work, these give just a little over 36,000 RAC running BRP on the GPUs with a small contribution from LineVeto Extended on the CPUs.

While these have mostly been pretty satisfactory, my power costs are considerable, and I've been throttling (using Fred's TThrottle) both to hold back room overheating in the warmer eight months of the year, and to reduce my top-tier power costs, which here at the moment run 14.7 US cents per kilowatt-hour when over 900 kWhr in a month, and not so very much less at the next tier down. My home uses evaporative cooling, which while less a power hog than refrigerated air, still gives me incentive to cut down PC power during the cooling months. A particularly undesirable attribute of the GTX460 for my case is that the contribution to system idle power is very substantial.

Gary Roberts has argued the case for the GTX650 as giving a good combination of performance, purchase price, and power consumption. I've recently considered re-equipping both GTX460 hosts with a GTX650 replacement. The power cost savings would recover the initial expenditure in less than a year, but my yearly average output would drop moderately. The small die size and perhaps the TSMC 28 nm process probably give the 650 cards lower idle power than my 460s, and of course the operating power is dramatically less.

More recently I'm thinking that for at least one of the systems I'd like to consider replacing the GTX460 with a GTX660 instead of a 650. On information I can find so far, it appears this would still give a system with somewhat lower idle power than my 460, higher Einstein useful throughput when running at full rate, lower maximum power, and a more favorable productivity per watt rating throughout the throttling range.

But I'd really like anyone here with GTX 660 Einstein (especially BRP) knowledge of any kind to share (experience, observation, reading...). Any information would be welcome--actual observed performance, power consumption, power supply sensitivity, driver problems, dependence on host CPU capability, dependence on motherboard bus capability... I don't mean GTX660 ti, which is another beast entirely, and I've not been able to find an appreciable number of Einstein hosts running the GTX 660 flat out.

My systems are not pure Einstein compute hosts. One is in fact my daily driver and also my primary sound editing platform. The other is the primary disk host for backups on my network, and also the backup desktop PC for occasions when my wife or I have trouble on our respective primary PCs.

I still intend to use a GTX650 if I do a new build for my wife soon. The current one has no graphics card at all, and the computer desk at that location provides inferior case air movement, so lower maximum power is a major consideration.