not enough info. whats your ghz? sins is single core, so 3 of thoese quads are useless, and if its trying to use the same core all your background stuff is using... i7? overclocking? we need more info.
sins will only use the first 2 gigs of ram (although, i do believe there is a fix for that somewheres?)... so if you are already using 1 gig of ram for background stuff, then you only have one gig left for sins. play with your settings.
i highly suggust you post the replay. 10 players playing distant stars mod, with 800 planets and maxed fleet supply will be laggy. or were you playing a 1v1? need info.
oh, and whats your internet connection? is someone trying to use youtube while your playing? that tends to make things laggy if your internet cant handel it. need more info.
And, the worst thing is when someone else in the game has crappy interenets, because he will slow everyone else down to a crawl, and no supercomputer you have will fix that.
Are you using vanilla sins? or diplomacy? diplomacy has significant inprovments over vanilla speed in memory usage and such. the same game in vanilla sins runs significantly slower than diplomacy does. need more info.