Ok, I don?t think there?s a head to head comparison that you can find, so how about this sequence (which focuses on games since that?s the intended audience):
C2D E6300>A64 3800+ (dual core @ 2.0Ghz)
The advantage runs between 5% and 33% depending on which game you look, at with the average @ about 15 %.
Link 1 Link 2 Link 3
Next, let?s remember that dual core doesn?t do much for most games, even the very newest games, so comparing to older single core processors is reasonably fair. And since we are talking about fairly old hardware, the only comparisons are old games.
With
this review of Doom3 from 8/4/04 you can see that the A64 3000+ (754) @ 2.0 Ghz is between 26-40% faster than a P4C @ 2.4Ghz, for an average gain of 33%.)
(Now granted, the two A64 chips are not prefect substitutes for one another, but for the sake of getting in the ballpark let?s just pretend that they are.)
So on a very rough level here?s what I come up with working from bottom to top
Your P4 @ 2.4 Ghz =1
1 x 33%= 1.33 (diff b/n a P4 2.4Ghz and a A64 2.0Ghz)
1.33 x 15% = 1.53 (diff b/n a A64 2.0Ghz and C2D E6300)
Soooo . . . I?d say,
at very conservative minimum, a C2D 6300 @ stock is 50% faster than the old P4 2.4Ghz. This doesn?t sound very exciting until you put it into to context where it has meaning. If you thought about it in terms of speed limits, a 50% increase of a 65mph speed limit means you can now go 97.5 mph! Here in the context of games, if you match the new CPU with a reasonably capable GPU, it will mean games will run that simply would not run before with details and resolutions that previously would have been impossible.
If I were a gamer with a P4 2.4 Ghz rig, I?d be ecstatic if I got any C2D rig with a PCIe slot to fill for Christmas.
Disclaimer for flamers: I know I made some logical leaps, left out the differences between the 754, 939, & AM2 sockets, dual channel memory, chipsets and that vid cards are a better bang for the $ than CPU?s for gamers. I was just trying to get to some kind of remotely justifiable percentage difference. Don?t flame, show better work.