Runtime differences between PCIe 2 & 3 while running 3 tasks on the same GPU at Einstein@Home:

PCIe 3.0:

GPU sec

3,172.46
3,015.02
3,129.75
3,051.46
3,581.70
3,333.05
3,497.01
3,262.41
2,940.57
3,341.89
3,138.30
3,140.32
3,220.97
3,032.34
3,109.77
3,093.44
3,236.33
2,790.31
2,582.41
3,257.33 AVG TIME FOR GPU= 3146.34

PCIe 2.0

GPU

3,659.54
3,765.54
3,701.79
4,071.55
3,488.81
4,000.56
3,806.07
3,685.78
3,171.36
4,354.94
3,593.30
4,214.23
3,516.39
3,680.21
3,731.63
3,816.37
4,183.45
3,451.99
3,748.91
3,723.35 AVG GPU TIME= 3768.28

% Difference= 16.5%

Even giving it a little wiggle room, THATS HUGE!!

Here are my rig's specs:

CASE: Corsair 600T Mesh
CPU: i7 3820@4.3
MOBO: x79 Sabertooth BIOS 0906
RAM: 16GB Corsair Vengeance 1866
GPU: GTX 680
COOLING: H70 CORE w/ Scythe Ultra Kaze in push/pull@ 2400/2200
Storage: Agility 3 2x60GB
PSU:Seasonic 750W Gold
OS:W7 Home Premium SP1

Since x79 PCIe 3.0 has been disallowed on NVIDIA's newer drivers, I had to edit the registry with a known hack in order to get this to work. Quite impressed.

Thanks for the report. 16.5% difference is a compelling reason to get IB before purchasing a GTX 680.

16.5% won't be the number for this project, since with 3 WUs crunchi, each.asking for CPU time its higher. But I do suspect a difference will be noticed. Possibly along the lines of skgiven's 4.5% guess.