Weird that I'm still so much faster on 270..

310MH/s at 1123MHz.
280x is about same speed as you or smolen, 510MH/s at 1150MH/s.
My miner is full sgminer with all algos working, works fine with multi-algo in nicehash.
That's not weird, that's good - at least, for Vanillacoin

The released kernel (exactly same binary) is getting 543MH/s with 280x, 4 threads, worksize 64, core 1150, mem 500 on Linux. I got last few MH/s by using more registers, perhaps it was wrong optimization for other cards. Old kernel is somewhere in archives, good occasion to implement --kernel switch and release it.