Bitmain hardware is awful.  IMHO the last good hardware they made were the S1s.  Everything from there has gone downhill.

As others have correctly stated, p2pool "restarts" the work a lot more often than "conventional" pools.  In layman's terms, the conversation between your miner and p2pool goes something like this:

p2pool: here is some work, stop everything you are doing and start working on this
miner: got it, I'll start working on it as soon as possible
(avg 30 seconds later): p2pool: here is some work, stop everything you are doing and start working on this
miner: got it, I'll start working on it as soon as possible

and so forth.  That "stop everything you're doing" part is what Bitmain hardware sucks at doing.  Spondoolie hardware seems to manage it just fine.  As always, YMMV.  Some folks have luck tweaking their S2/S3/S4/S5/Swhatever, sometimes regularly.  I never had any luck with it, and have long since given up on Bitmain junk hardware.

For comparison, conventional pools look like this:

pool: here is some work, switch when you can, I'll continue accepting your prior work for a while
miner: got it, I'll start working on it as soon as possible
pool: here is some work, switch when you can, I'll continue accepting your prior work for a while
miner: got it, I'll start working on it as soon as possible
pool (approx ~10 mins): here is some work, stop everything you are doing and start working on this

M