What GPUs does your site consider?
My website only considers GPUs which do not have a problem I call "hashrate degredation." I don't know if there is an official word for it, but that is what I call it.
These are cards like the GTX 1050 ti, GTX 1060 and 1070, and 1080. Actually, those are the only cards which I have seen without this "hashrate degredation." Almost every other card has this problem, and eventually the gtx 10xx will have hashrate drops too.
Cards like the RX 480/RX 580 and R9 Fury drop in hashrate each DAG Epoch, so I do not consider them in the website's calculations. My website would be extremely inexact if I did.
What is "hashrate degredation?"
It is the decrease in hashrate a card experiences as the DAG grows. The DAG is a big chunk of data GPUs use to mine Ethereum. The bigger the blockchain though, the bigger the DAG. The bigger the DAG, the lower the hashrate. If the hashrate drops then your profits drop. Some GPUs keep their hashrate better than others with the DAG growth.
What cards have this issue?
Unfortunately almost every card, including the RX and R9 series cards (Except for the R9 290X, Yay!). I have an RX 480. When I got it about 3 months ago it did about 22 MH/s. Now it does 18.2 MH/s, and it gets worse each time the DAG grows.