And if you total the network hashrate for all of them *COMBINED*, I'm pretty sure they are well under 20 percent of Ethereum total network hashrate.
Is there a place where this can be checked? It would be interesting to see what is what.
There is also the factor that by the time ETH goes full POS, there will be at least one new "even more efficient" generation of cards out from Nvidia, might be a new generation out from AMD, and the E3 is already going to be struggling to compete before the big "profitability falls off a cliff" event happens that the move to full POS will cause.
So how different is this scenario where "even more efficient" GPU card is released for mining compared to a new ASIC miner is released for mining? Each new technological breakthrough will leapfrog the previous generation/solution.
Whether a new GPU based miner arrives or a new ASIC based miner arrives, the impact to the network is essentially the same. Owners of new miners will enjoy the benefit of "even more efficient" mining while the existing miners are pushed to become "less efficient" miners. As a small miner I can't compete with those gigantic farms. For me, it's irrelevant if they are using GPU or ASIC miners. My mining efficiency keeps on decreasing with a startup of another large mining farm or an introduction of new "even more efficient" miner.