I'm running:
2x ASUS OC 750 Ti
2x MSI TF 750 Ti
2x EVGA FTW 750 Ti
EVGA are the best for me.
Running two windows windows concurrently with these settings: -H 2 -i 0 -C 1 -T5x24
Gave me 40-60 kH/s boost across six cards to push me consistently over 1800 kH/s. I still need to re-tweak the ASUS cards as their OC is low and not optimized.
http://cdn.overclock.net/5/55/900x900px-LL-55c670d9_RunningtwoWindows.PNGThe main point of showing this is that I have been able to recoup some of the "lost kH/s" from the "cudaminer riser bottleneck," but not all of it. Some of these cards will do 340 kH/s when plugged into an x16 slot directly and using the -H2 flag.
I have bought one of these babies:
http://amfeltec.com/products/flexible-x4-pci-express-4-way-splitter-gpu-oriented/It is an active x4 to 4x x1 bridge. They use PLX silicon, so it should be legit. I am getting the sku that allows me to power the card on the "adapter" boards. I have purchased four SATA male to FDD adapters from monoprice and plan to use cards that have a six-pin PCIe power header to make sure I'm not pushing too much current through the adapter board (better safe than sorry). The ribbon cable between the host and adapter board is 3.3VAUX and signals ONLY, so we don't have to worry about melting ribbon cable riser cables. smile.gif
The host to adapter board pinout is GND, PRSNT, TX+,TX-,RX+,RX-,CLK+,CLK-, RST,AUX3v3
If any of you guys who have 4+ rigs under your control and have found a cheaper solutions towards a PCIe bridge/extender, please let me know. I think that this may be one of the best ways to do it.
I confirmed that on my Z87-PRO MB that the first two x16 slots will operate at up to x8 link width while still working with four additional risers. Adding this PCIe extender will allow me to run 9 cards on one motherboard. Theoretically, I could purchase an additional extender and run 13 cards. I will be interested to know what limits I hit with Windows 7x64 + Nvidia driver. I figure after I hit 8 GPU's, I'll need to switch to Linux. It will be interesting to see how things scale with Cudaminer today. I believe that this is how we make the 750 Ti scalable to compete with the higher hash-rate density cards out there on the AMD/ATI side.
C
