Okay, I connected to port 5555 on your pool about 15 minutes ago and difficulty seems to have topped out around 40000 and is oscillating between that and around 19000. 40k is still high for ~720 H/s, but it's a lot better than the >200000 it was soaring up to - and staying at - on ird.cashpool.us. I would say you have a workable and acceptable vardiff implementation; the best I have seen for a Cryptonote pool, actually.