Which setup will run better (4 mixed DIMMS or 2 matched ones)

Basically at the moment I've got 4 DDR3 DIMMs installed, 2 are 4GB and the other 2 are 2GB .. All 4 run quite happily at 1600MHz with sum decent timings too..

But would just 2 8GB DIMMs be better?? The cheap ones I was looking at are still 1600MHz but with timings of 11-11-11-28 .. The more expensive option has timings of 9-9-9-28 but I don't really wanna spend that much ..

Is the way my RAM is setup having any effect on performance?

Cheeers

In general 2 dual channel DIMMs are best, real world I doubt there would be any meaningful improvement.
You could post screen shots of your RAM profiles, which would give a better idea of performance.

Basically you get diminishing returns over 1600 speed.

No, a friend of mine has been running 3x4GB and 3x2GB on his 980X and he has never had a problem.

I'm not having any problems, was just wondering .. Here's a shot of the speed n timings the 4 DIMMs are running at..

The differences between the two different kits isn't much and all 4 DIMMs are auto set to their XMP-1600 settings..

Set # 1 :- Corsair CMZ8GX3M2A1600C8 - 8GB Kit - 1600MHz - 8 - 8 - 8 - 24 - 41 - 2T @ 1.5v
Set # 2 :- GEIL CL8-8-8 DDR3-1600 - 4GB Kit - 1600MHz - 8 - 8 - 8 - 28 - 37 - 2T @ 1.6v

So all 4 DIMMs are running at the Corsair kits XMP settings, I've set the voltage to 1.55 and it seems stable enough

As long as it's stable, it won't have any impact on performance. The problem with mixed DIMMs are usually getting them stable in the first place. If you've gotten them stable and are happy with your speed, timings & capacity, leave well enough alone. The advice given is usually to go with matched sets to prevent compatibility / stability problems when people are building new or expanding. If you've already got them and they're happy, you won't see any performance loss.