I agree Mannyg, once they connect they're fine, no issues, but if you restart... Also, I have my 280x hashing around 2.6Mh on 14.6 beta drivers in BAMT. I use the same settings for x11/x13/x15, the below conf is for my Sapphire Vapor-X 280x.
"intensity" : "16",
"worksize" : "256",
"thread-concurrency" : "8192",
"gpu-threads" : "2",
"gpu-engine" : "1080",
"gpu-memclock" : "1450",
"failover-only" : true,
"no-pool-disable" : true,
"api-network" : true,
"api-listen" : true,
"api-port" : "4028",
"gpu-powertune" : "0"
Sure wish Nicehash would chime in and let us know what is up with these connection issues!
Seems to vary a lot with driver version, my 280x only getting about 2.1 MH/s with pretty much identical settings. I'm on 13.12 still, not sure I can be bothered to play uninstall/reinstall/reconfigure-all-the-displays games right now though..
I've read that the 14.4 drivers increase X11 hash rate, and the 14.6 ones break everything without some voodoo file swapping and modding, etc. I dont want to have to bother with all that nonsense, it's very frustrating to not see a straight forward driver install for my GPU's and have everything work the same as with 13.12.
I've started to notice a new thing too, ... occasional random HW errors popping up on X15. Same configs i used with X11 and X13 that didnt have HW errors at alll... ever.
Does thread-concurrency matter for X11/X13/X15?