I see that the diff doesn't go above 0.8.
A highend rig that does 3.4GHASH has the same diff as a 1.5GHASH rig. You should increase the difficulty to reduce the load on the server.
you can set manual static diff AFAIK. But nevertheless better to start your own stratum and go solo ))
The autodiff is bether today, I get fewer rejected shares and the pool seem more stable.