Graphics Where's the bottleneck/difference?

Artanoon, all!

Right, before people go jumping in with sarcastic comments, I do know there is a marked difference between the GPUs in my question (to follow) but I'd like to understand why/where it is as I'm not fully clued-up on the techy side.

So, to the question then. I've got a pair of 670s in SLI and I was looking to see what my next sensible upgrade would be (more out of interest, since I'm not using them at full potential right now anyway). I went on Wikipedia to get the specs and release dates for different models just to see what the differences were and I got a bit confused.

An original Titan for example, is listed as having:
14 SMXs
837 MHz Base clock
40.2 GP/s pixel fill rate
288.4 GB/s memory bandwidth
4499.7 GFLOPS

and the GTX670 has:
7 SMs
915 MHz Base clock
29.3 GP/s
192 GB/s memory
2459.52 GFLOPS

Now, I know the Titan whups the 670, but why does it still beat two in SLI (assuming it does)? What is it that stops SLI just doubling the 670 stats? There must be a bottleneck somewhere, otherwise nobody would buy Titans for example, but I'd like to know where.

Grateful for any educational assistance!

 

SLI and CFX look great in fake benchmarks like 3D mark for example and timespy demos. The reality is different.

All games require drivers to deliver optimal performance. SLI and CFX both need drivers designed for each game that you wish to play.

Certain titles will never get this support. The older the title the more likely hood SLI and CFX is to work.

 

SLI support in reality isn't very good for a great deal of games. Even big budget AAA games sometimes get no SLI support. SLI as rollo said looks great in benchmarks where SLI has specially been implemented, reality is different.

 

IIRC 670s in SLI are about 10-15% quicker than a Titan. That was why all of the boys with the 690 sighed relief when it came out. I was using two in SLi when it launched, hence why I remember.

However, these days things have changed. SLi is no longer being supported properly, if at all, and Kepler is being derped rotten in the latest drivers. Now before any one jumps down my throat I will just say this - GTX 950 beats GTX 780 in most current games. That should not be happening, so it is clear that Nvidia are not optimising jack for Kepler.

 

the slowdown/difference comes from if the game and drivers and the planets align and tasks can be divided between cards reliably and successfully...

If it can, then as VT says you should get a performance bump over a Titan
If it can't divv things up properly, then at best it'll be slower than a Titan, at worst the second card will sit idle and you might as well not have bothered [worse still, the drivers could **** it up completely leaving with less performance than with a single 670].

For most scenarios and users, a single faster card is preferable to hoping the stars align and it all works, and certainly preferable to the ballache when it doesn't work.