I actually run an S2 on p2pool - I've spent literally days tinkering around with the settings and found that the best settings for my setup was to use --queue 0 --failover-only mildly OC'd to 212 which gives me ~950Gh/s compared with ~1100Gh/s at a centralized pool.  It's not the best & a bit of a power draw, but I'm happy pointing it at my p2pool node with the rest of my miners 

Oh for a decent firmware update......