Ok, so I'm shopping around for a new GPU. I'll likely go with an nvidia gtx6xx series card, but I have some reservations about choosing the right one.

Basically I'm concerned about the performance/dollar ratio, and whether selecting a card with a 256-bit memory bus is going to net an appreciable gain over a card with a 192-bit bus, all other hardware specs being equal.

I find it ridiculous the granularity of decisions one must endure, but one can easily purchase two cards with the same memory and core frequencies, RAM size, CUDA core count and so on. My question is "All other specs being equal, does the larger memory bus equate to more BOINC performance?"

If it turns out that the larger bus is significant, or at least appreciable, then does it pay better to buy the card with the larger bus, or the smaller-bus card with more RAM and/or higher clocks?

OR should I just say to heck with it and flip a series of differently-sized and -weighted coins (for adequate entropy) to decide on which card to buy?

If performance/dollar is meant as Performance/power bill than te GTX 690 offers the most GFlop(SP) per Watt tdp (18.74)
and that is a figure not a single AMD card can deliver (mind you: the HD 7990 goes up to a ratio of 28.00). GFlop(DP) is quite another story. When you're into projects that favor DP performance (e.g. MilkyWay -prerequisite there even- or some PrimeGrid sub-project, or WCG-HCC), then I'd recommend a HD 7990 (when affordable) or a HD 7970. Given two cards with the same GPU, go for the one with the higher clocked GPU, then go for the wider bus and as last the biggest memory.

JCMarsh, please be mindful of the cost to run as well. I was a little shocked at my utility bill. I set up a system with three Nvidia GTX OC 570 GPUs. After I set up this system, I thought the first months utility bill was a mistake. After 3 months, I essentially stopped running my powerful system more than 4 hours a day. Silly me.
Mike Barnett

I asked a similar question on the BOINC GPU subforum and haven't gotten any constructive help so far. I think my question is similar enough to piggy-back on this thread.

The primary use of my GPU will be for BOINC, although I still need video out so I can't go with a "headless" model like the Tesla. I have four PCIe 2.1 x16 slots available, so I can potentially upgrade later to multiple GPUs. Looking for most BOINC-for-the-buck, primarily with respect to initial purchase price. Power efficiency would be nice, but will only be a tiebreaking factor (I don't pay the power bill). Heat generation (which is related to power consumption) is more important than total power use. I prefer nVidia products. Any benefit to going with a Quadro series vice a GTX series card?

Thanks in advance.