I have a question about using the suggested diff setting for my miners. I have 2 antminer s3's that I'm using in the pool under one payout address. Up until this point I have not set the diff and noticed my charts have large spikes. I've read mixed reviews on setting the diff. Some people have stated that they noticed a larger number of stales ect when specifying the diff. Should I be setting the diff for this pool? If so should I be setting it for 256 or 512 because I have two workers on one payout address?
NastyPool pays out based on detected hashrate. It does not matter what your reject rates are. The important thing is the hashrate NastyPool detects matches the hashrate you expect from your miner.
If you have 2 antminer s3's mining to the same address using the same miner username and host and port then you should see the average hashrate on the miner page
around 900 GH/s (450 x 2). If that is the case then you do not need to concern yourself with anything else.