Hello! Thank you very much for your replies!
Just for an historical perspective, all DAG were always requireing a 2Gbs card and will soon grow to need a 3Gbs? Furthermore the hashing speed is very dependent on the bus size?
If i'm right, DAG file size change every 5 days for ETH.
And some cards suffer more with this growth especially old cards.
For exemple, my 7970 are loosing hash at every DAG change
But it seems that R9 280X ou R9380X that are just evolution of the 7970 suffer less.
And new cards like R9 390 or Fury / Nano are not impacted with the DAG file change.
My oldest card doing 20 Mh/s in november 2015, now it's 17Mh/s
In this time, my full rig of 5 cards was hashing @98Mh/s, now it's 93Mh/s (Some cards lose less hash, I have different model Sapphire, HIS, MSI ... and different RAM on them)
I guess that in 6 month, I'll hash something like 90/88 Mh/s with my old generation cards
But they have already ROI multiple times and was buy used at low price (~130-140$/card), so it is a good thing
If you could buy a cheap 7950 or 7970 3GB for your gaming desktop, It not a bad idea.
Or invest in cheap R9 290/390 when next gen GPU will be out in Q3 2016
