Well I went with a 2nd hand 280x instead for only $10 more than the cost of the 280, so now I have 2x 280x
Both on stock bios and stock clock settings with AMD 15.12 Drivers I am getting from 168-180 sol/s on average with intensity set at -i 2 on the both of them.
I tried -i4 and it was a bit more powerful but after a little bit 1 GPU dropped off in hashing after a while to just over 110 sol/s until I gave it a 1 minute break and restart, I also tried -i 0 but only got 140-150 sol/s
Even at intensity -i 2 I still get the occasional drop in hashpower on the same GPU that requires restarting of the miner and then things go back to normal which is weird.
350 sol/s from 2x 280x I am happy with, now I just need to test how many Watts it draws when mining.