I’d recommend 2 780s, it can be nice having a separate videocard for rendering the UI without being fully tied up in rendering. And when you have it running with both barrels, I bet it will still render faster.
You shouldn’t listen too much to me as it’s been a long time since I last bought a computer (and none of those cards were available at the time). Nvidia says both cards have a two slots width, so might have to make sure there is space enough for them on your motherboard if you plan to use two. A quick note was that the titan has 6gb of vram while the 780 has 3gb (using two won’t let you combine the memory resources - the limit would still be 3gb). That would be very important if you would end up in a situation where the titan can fit your scene in memory while the 780 can’t. I would expect two 780s to be faster though for scenes they can handle (http://www.geforce.co.uk/hardware/desktop-gpus/geforce-gtx-titan/specificationshttp://www.geforce.co.uk/hardware/desktop-gpus/geforce-gtx-780/specifications). How likely that is to happen I don’t know, as I don’t know what kind of work you do. I have not compared prices at all so I guess you’ll have several things to consider.
Two GTX780s will be slightly faster than a single Titan, but you lose 3Gb of vRAM. (Take note that 2x780s is not 100% more power compared to single 780, it`s something like 70-80% additional power for the second card). I would go for more vRAM any time of the day and you have a free slot for possible second Titan in the future.
Cores count but also their speed the memory bandwith the precision of the chips etc.
Thats why 500 series are faster than 600 series cards while the 570 has 480 Cuda cores with 1464 MHz and the 670 has 1344 cores with 980 MHz.
They make cards for gaming or GPU rendering but dont want really cards to cross over into each other …
I also read about that somewhere here too in some older thread that I dug up while researching best hardware for Cycles, but I don`t have time to find it right now.
EDIT: Systemagnostic guide does not take into account Titan and the 700 series so the advice for buying the best card is a bit outdated. Other than that the guide is probably best documentation about Cycles hardware side.
2 GTX 780 have in total 4608 processors
1 titan is 2688 processors
So obviously 2 GTX780 would be what I would buy
But I would like to know a benchmark with the 690. The 690 has 3072 processors. I would like to know with current blender buildbot the 690 versus the Titan. My guess is the 690 would win, but in the benchmarks I don’t see that and my guess is perhaps they were using different blender builds. I can’t believe the titan win the 690
A 670 has 1344 processors so two would be 2688 processors. Same as the titan. But much less than 2 780 that have 4608 in total.
@zeealpal After reading some more about multi-GPU rendering processes, you might be right on that one. It seems that the FAQ is a bit incorrect on that part and it actually talks about SLI, not multi-GPU setup.
All i can say is when you do upgrade, Any chance you can donate me me your old gtx 560ti lol. Im working on a open gl physically correct material system renderer but im poor and only have a AMD card right now, need to find a kind person to donate a nvidia card for cuda parts of code. A could muster a few quid but that would be just about it, rent and bills are killing me right now.
According to benchmarks, the Titan is about 20% - 50% faster than a single GTX 780. Performance wise, you will be faster with 2x 780s. However, they will limit you to 3GB VRAM. You will also need a PSU capable of running 2x 780s and have a good airflow in your case. Probably, you might also have to deal with drivers and problems in other applications than Blender. You should keep in mind, that you already hit 1GB with simple tasks. 3GB will give you some space, but a Titan will be better. Also, Nvidia is limiting GPGPU speed for their GeForce graphics cards (this is one reason, why the AMD HD7970 easily outperforms Nvidia GeForce cards in OpenCL tasks), because otherwise they would compete with their own, much pricier Tesla boards. I don’t know, if this limitation also applies to the Titan GPU. Judge for yourself, whether it’s worth the trouble going for 2x 780s or just sticking with the Titan. Here in Germany, you can get a Titan around 900€ vs 2x 780s for ~1200€. Going for the Titan and saving the money (or investing it into a graphics tablet, a decent GPU for viewport (so the Titan is only used for rendering) or whatever) is imo a good option.