Running 6x Gigabyte GTX750Ti OC cards on an Asrock PRO BTC board here. Using the USB3 powered risers for all 6. I haven't modified the BIOS so the stock limit still applies. At the moment I just have +180 core and +400 mem set in MSI Afterburner (gigabyte OC Guru is limited to 5 cards...). That's 6200MHz memclock. The power limiter seems to keep the core clock in check anyway, so I don't think it's ever actually getting to +180 core. With chrome open, I'm getting *just* under 300kh/s per card.
PSU is an In Win Commander II 1200W (overkill for this, but I had one spare). It's 80+ Bronze rated so ~85% efficiency on 240V supply. Idle is 65-70W and full load is 450W. Works out to 54W of actual DC power draw for each GPU plus whatever the tiny idle amount is.