Wow! I'm impressed with the large savings you are making by tweaking your BIOS. switching off firewire for 5W, man! When I switched off firewire the only detectable difference was that the firewire port wasn't lit up, the power drain didn't change at all for me.
In this case I stand corrected and do absolutely set about tweaking your BIOS as much as you can. But even so, the efficiency of the PSU could save/cost you 50W so is worth considering at least.
I'm afraid I can't advise on PSUs. I only have one miner and I bought my PSU with noise as the primary consideration. For me the PSU is critical in building a mining rig (along with the cards and motherboard). The chip, drives, RAM, OS, et cetera are good to get right but of secondary importance. I personally never skimp on the power supply but for maximum profit you may want to go with something cheapish which can manage 86%+ at your mining load. A typical positive attribute and one many people pay a lot for is for the PSU to be at least x% efficient at any load - give that you really don't need this shop around and look at the efficiency vs. load graphs for cheap PSUs.
As for voltages on the cards it really depends what you want out of your system.
- To maximise MH/J you will probably want to drop the voltage quite a bit (0.1V or more) and a little more still if you have many cards in one rig.
- To maximise profit then you may want to overvolt your cards by a small amount (0.05V is my guess) but this is assuming you have cooling sorted.
- To maximise MH/s then I find 1.25V is best (higher voltages hurt my stability due to the increased heat).
Of course, there are many factors: The cost of power; The market value of bitcoins; Your cooling; Your noise tolerance; How good at overclocking your particular cards are; even the OS! I would get a PSU which is efficient at the power you expect to draw and for +/- 30%, use a power meter to measure power consumption at the wall, find your maximum stable clocks for a range of different card voltages and note power consumption/temperature/noise each time, and the calculate what works best for you.
If MH/J is important to you then let us know how efficient you manage to make your rig. Mine is at 2.41 Mh/J. My PSU is 89% efficient at my load, I'm running off of a HDD, and I'm running two Sapphire HD5850 Xtreme cards.
Actually most of my tweaks are done within windows,only the disabling of unneeded chipsets can be done at BIOS level such as the disabling firewire and other things.
As I have an Asus mobo,I can use a utility called EPU-6 which lets you tweak CPU clocks (as RAM clocks auto change with CPU clocks),changing fan speeds (full blast to silent mode),under volting and underclocking teh chipset itself,manage HDD times before shutting off,overclocking is enabled at turbo so you can overclock and underclock quite well with this utility.
It's best to enable 'green ethernet' with your device manager in windows (that saved me quite a bit) as it only switches on when network activity is there,it can also vary the power used based on network activity,think of it as the speedstep for the NICs.Power varies based on network activity and how long your cable is.Normally a NIC is running at full power regardless of what its doing so you're wasting power when it's doing nothing.
Is Silverstone a reputable PSU make like enermax? As I have to make sure that the PSU I buy doesn't fry my system like the 1 on my first comp did in early 2007 (That comp lived from 2004 til early 2007)
Thanx tho guys for the tips so far.