I am offering a 20000 einsteinium bounty to the first person who can help me solve this problem. I have the exact same rig setup as my friend minus our motherboards and internet service providers. I am running two rigs and he is only running one. We are mining on the same p2pool as well. In a given day I am receiving about 3000 emc2 running with my two rigs while he is receiving about 20000. Each of his payments are 300+ today while mine are only currently 40-45. Please let me know if you need any more info. I will be glad to provide it.
he could be using a different mining software, have higher overclocks, and maybe he is also cpu mining. use this miner http://k-dev.net/cgminer/ and try to find a listing of your card here and mimic their settings to get the highest output you can. https://litecoin.info/Mining_hardware_comparison
another option people talk about is using http://guiminer.net/bamt this is a dedicated mining OS i've heard people getting better results using their software.