There's so little between the two (comparison: click here) the 6000+ PC seems better value. For the difference, you could add 1-2Gb of RAM (click here / click here) or even get a better graphics card, if necessary. If I was mainly a gamer I may go for the E6600, otherwise the 6000+ would be more than sufficient.
The 450W PSU doesn't look good in the Matrix i67N88-VSTA. It received a very good review by PCA click here - no mention of the PSU though. Do you have a link to the system? G