I get also only rejected with cgminer 3.1 and the second problem is that first gpu runs at 50kh/s and second 550kh/s whats the problem there ?
do you have scantime = 1, expiry = 1. it helps while blocks are being generated fast.
What do this settings especially do ? Should I use it always on all coins ?
it tells how long your threads look for a solution before requesting new work. if a block comes in every 2 seconds you want to keep this low. with blocks that come in once a minute, it is not necessary to set it so low.