not really a ideal benchmark because of the differences of p2pool and PPS. as you could of been mining during a lucky time for the pool hence higher rewards. also got to factor in pool fees. for example next week the results could be much closer..
p2pool should always beat PPS on BTC Guild in the long run. That's the trade off you make for PPS: Steady income at a high fee vs extremely random income at low/no fee.
A much better benchmark is comparing BTC Guild PPLNS to p2pool. But even then, as zerokwel pointed out, luck is going to be what determines anything. In the extremely long run, p2pool will win (low fee). But BTC Guild will be MUCH more steady from week to week. It's up to miners to determine how much steady income, management interface, email alerts, etc., are worth to them.