You may get more responses if you posted this in GH. but as far as I'm aware, the mobile Bartons are just regular Bartons with their multipliers unlocked and have been picked to be able to run at the same rated speeds on lower voltages. Therefore:
1) clock for clock, they should perform exactly the same
2) newer Bartons are multiplier locked; the mobiles are unlocked, since that's how laptops do clock throttling to save power. older bartons should also be unlocked, if you can find them
3) OC'ing results can always differ, but since the mobile parts are supposed to run at "normal" speeds using lower voltages, you can probably already push the mobile 2400+ pretty far just by bringing it up to "default" voltages (1.65V). so the mobile 2400+ would probably give better results than the regular 2500+.
4) dunno, sorry
-asp