You're KIND of leaving the p4 open to guess here, because you're not really telling us much about the cpu.
Offhand (and following
THIS chart, i'd say the x2 4400+ would be MUCH faster, but again, you're gonna have to specify just which p4 2.8ghz cpu you have...
But yeah, the x2's gonna be faster. If you decide not to use it, PM me and we'll arrange something else!
