I am not sure why people are so obsessed with vardiff. Changing the difficulty of submitted shares does nothing to find blocks faster or slower. I was fine at middlecoin with diffs of 1024. The pool doesn't get paid by shares, it gets paid by blocks. I just like the website here better.
Because we have one crappy card, and 516 is too hard for shares.
What is your gpu? I got r9 290 with 883 kh/s mining in middlecoin. I mined yesterday in middlecoin for 24 hrs now and my Total BTC in a day is 0.012. I will switch to this pool after it is stable.