The Cache isn't what gives away whether it's a barton core or not...it simply depends on the manufacturers whim really and it just so happens they decided to make the 2500+ XP and 2600+ XP from the same core as the 3200+ XP, besides that the program CPU-Z will tell you what core it is.
It really depends on how good your cooling is man. How low your temps are things such as that. Also you gotta consider things like how well your RAM will take it and also if you don't have an AGP
CI Bus lock then you won't be able to up the CPU FSB otherwise once you go too far you'll fry your AGP and PCI Components so be weary of that. Other than that, whatever speed you can get it stable at while remaining in 40's Celsius in temperature with a full load temp of low 50's I'd say you're in the clear....
the 35w mobiles have insane Overclockability though, more so than the 2600+ XP, I have the 35w 2400+ XP-M unlike the 2400+ XP this has 512mb L2 Cache, and runs at half the wattage...I got mine overclocked to 2.7GHz prime95 stable for 12+ hours, but I've since backed it down to 2.5GHz just for cooler temps and a lower Vcore...
All in all you should ATLEAST be able to hit 3200+ XP speeds with good cooling, but like I said without an AGP
CI bus lock you can't up the FSB without frying components...only way to OC would be to raise the Multiplier.