Well basically it's better than any XP hands down. Since the top XP is the 3200+ at 2.2GHz and I have mine at 2.5GHz then it beats it out as far as clock speed which is basically the definitive test as to which is better because both this mobile and the 3200+ have the same barton core, L2 Cache, and all that jazz.
If I clocked my XP-M to 2.2GHz then technically it'd just be the same as the 3200+ XP, but like I said that extra GHz basically makes it better than any current XP.
As far as P4's go I really don't know enough about Intel and their processors to fully answer that. And the last bench I did was quite some time ago with my CPU up at 2.7GHz, heres that screenshot though:
It can handle itself pretty well against some P4's which clearly have a much larger clock speed, however, if you look the Integer bench beats the 3.8GHz Intel, BUT it doesn't beat the floating point bench, so it's kind of a trade off.
Either way it still outperforms a good amount of Intels above it's class. But once you start getting into Platinum EXTREME EDITIONS! or whatever pentium has right now then of course they would obviously perform much better.
As far as 3dmark is concerned, that's all GPU basically so that really has no coorelation on the CPU although yes it does test the CPU a little it really doesn't reflect too heavily on the actual score.
I think I get like 3200 in 3dmark because I only have a FX 5700
Hope that answers it enough for ya