Hey, just a short heads up .... First of all, i don't think it's the right time to buy gpus or upgrade rigs, seeing ETH2 coming and the ROI of a gpu being at least 1 year or even more... See, i flipped all my 580s a year ago for RTX3000series V1, at that time the ROI was about 3 month, so i made profit for about 6-9 month now and didn't even consider investing it into new hardware because the ROI since may 2021 rise 4 times!

But still if you want to buy gpus, why do you buy 6900XTs!? the have the same hashrate as 6800xt or 6800 and draw way more power!? The are not power efficient at all!!! 2x6900xt are about 130mh/s and draw 300 to 350 watts, further there are no bios mods if seen working (like the old 580 bios days) and oc/undervolting is a pain in the ass... at least compared to other gpus. The 6600 or 6600XT are as power efficient as the RTX3000series V1, if you want AMD i would consider those, even if you need more Riser/Pci-e power, at least if you have enough mainboard connections available. If not try to get some used powerful RTX 3000series V1 or 5700/5700XT if you want to stay AMD. But watch and research the gpus power/hashrate efficiency!!

But again, at the gpu prices these days, ROI is high, the only profit i see is holding your mined coins and hope for higher prices to sell, but then you should just buy coins atm and don't bother mining... If mining is and hobby you enjoy, then go for it and have fun, but don't buy the wrong gpus, do your research!!