Custom roms should give you a nice boost to around 480Mhs, thats alot of pretty much free hashrate.
My 16 cards are doing 465Mhs @ ~2900w
I don't like to push my cards that hard.
I think stock settings are safer. But I guess overclock could be okay since the cards have warranty.
The thing is that i dont think the cards are pushed that much harder.
My 470s have fans set at 55% holding around 70 degrees celcius @ 27.5Mhs (Mem oc to around 1950Mhz)
Warranty is no problem, i have got several gpus replaced after sending them in with custom bios onboard trough the years.
My rig is rock solid and have been going for over a month now with custom roms. More 470s on the way, will stop at 20 cards in total/580Mhs
What is the brand of 470s do you have? How did you OC them? I am getting 20Mhs with my MSI RX 470s.
I run Sapphire RX 470 4GB Reference with backplate, the cheapest one. (custom rom with 1500 strap timings)
Using wattman to oc mem, all the rest default.
I did want to clarify something you mentioned before about the 4-pin molex/2-per string comment. I just inventoried the cables that were included with my PSU and I have 2 with molex connectors... 1 has 3 and the 2nd has 2. So, what you were saying is to ONLY use a max of 2 per string, correct? This should work fine since I will at max have 4 off-board cards, so I will just leave the 3rd molex empty on the cable that has 3.
the cards may draw up to 75 watts per molex, so two would be 150 watts per string. this is generally what is considered the max for a string. so 4 cards, two per string with the molex connectors. for more cards you can use a sata to molex adapter but again only two per sata string.
The other thing that I was wondering about was the 8 pin (6+2) power cables that plug into the top of the GPU's. For instance, I know that I certainly need to connect this 8-pin to my on-board GPU in slot #1. But, will the other 3-4 GPU's connected via the USB x1 to x16 adapters also need this 8-pin power connected? If both these and the molex are required for each of the off-board GPU's, will this increase to total power draw per card by a considerable amount?
each card needs the molex and all 6+2 sockets filled.
some motherboards also have a molex socket on the motherboard, probably near the slots (gives more power for the slots) but i dont think your motherboard has one.
I run one card per string using molex directly connected to the riser, no sata connector between because they tend to get hot and melt. My cables dont even get hot this way.
I do this on my 470s + 480s rigs.
Powerdraw from the wall with custom bios:
470 4GB ref @ 27.5Mhs 145w
480 8GB ref @ 30.5Mhs 170w