Should I add an 8800 GTS to current rig?

[MindCrime]

My current rig is my daily driver, it crunches about 23 hours a day on average. I have an 8800GTS 640MB (https://www.asus.com/Graphics_Cards/EN8800GTSHTDP640M/#specifications) (i think it was the sleeper of the 8 series) from an old non functioning s939 opteron build that isn't doing anything and I want to know if it is worth the trouble to add a third gpu to my current system. So here is my current system details

win 7 64bit
i5-3570k max clock ~4.2ghz (hd4000 igpu runs opencl1.2 apps)
8gb DDR3 1800mhz
nvidia gtx 560 (non ti, stock clocks atm) I've been trying to set my projects to only use this gpu if they have a cuda app. Haven't done much research but the system seems to slay cuda apps compared to CPU and openCL apps.

Oh most importantly the motherboard is an ASUS z77 sabertooth (http://www.asus.com/us/Motherboards/SABERTOOTH_Z77/#specifications)

I remember something wonky about the pcie slots speeds when using more than one gpu in the manual, im not sure if that was only 1 slot specific or all or SLI, Xfire functionality. I guess my question is: Is it worth installing? Considering, is it supported by any boinc projects, are those apps going give any respectable results in contrast to the gtx560 and the i5-3570k. Oh my PSU is a corsair AX650. It's fully modular but I'm concerned I'd be pushing it's limits if I were crunching on all that hardware.

Let me know what you guys think and if you can share any experience, thank you for your time.

[John P. Myers]

It'll be fine. It will crunch but keep it away from GPUgrid since you're penalized if you take too long. Your power supply can handle it and your mobo will be fine as well. Putting it in either PCIe slot will be fine. If you stick it in the black one (i suggest this one) it'll run at x4. If you put it in the brown one, it'll run at x8 but drop your 560 to x8 from x16. It doesn't matter though since x4 is more than enough bandwidth for crunching with an 8800GTS.

[DrPop]

It's a good thought, and several of us have done it from time to time - add in an old GPU - to get the max credits on a challenge or something. But here's where I look at it, and that is: what are your electric rates like? If electric is cheap where you live, then why not? A credit is a credit. If electric is high where you live, I would not crunch with it, and rather sock away $20 per month for a while until you have a nest egg toward a newer GPU that you can score a good deal on used.

That 8800 GTS is going to give you roughly 3.5 times less credit per day as your GTX 560 Ti does, and take almost the same amount of watts to do it. Or in other words, your GTX 560 Ti is around 3.5 x as efficient. When you crunch 24/7, and the rigs are on your own power bill, then at some point you do have to look at the efficiency of what you're running. :)

[MindCrime]

Wow... Mr. Myer's response gets my hardware juices going but DrPop also brings up a good point. You know what, I think I'll let it go at shipping costs to any cruncher that wants to pay the power bill. I would much rather be ready for the new maxwells, or maybe an AMD APU build would be fun. Check the for/sale/trade for an 8800 GTS.

[conf]

Would be better to buy a new card cause of the power bill.
I have a 8800GTX lying around, its simply too expensive for the credits it makes.

[trigggl]

I would only use the 8800 on Poem, maybe Distrtgen. Anywhere else isn't worth it.