yes, the 10-15% only implies raising the fsb, w/o touching the multiplier.
unlocking the cpu is good, as you don't get into raising the fsb, which will keep everything cooler (except cpu!)- not sure how much you can raise the multiplier, which will be an experimentation with monitoring temperatures, and stability.
there is a difference between older durons (spitfire?), which are ceramic, and can be unlocked by the pencil trick, and the newer durons (morgan?) that are constructed like the xp cpu's, which need a more involved procedure to unlock -ie. fill laser cuts of l1 bridge w/ super glue, and then clean up bridges, and use some kind of conductive laquer as follows:
http://www.tomshardware.com/howto/01q4/ ... index.html
i would seriously consider unlocking the multiplier myself, as the frequency will not have to be raised in order to get the cpu going faster- perhaps raising the fsb as well, would be good for overclocking the video card as well (need for faster frame rates)- you'll have to decide/ experiment and monitor the system just to see what you can safely do before raising the voltage of anything (ie. cpu, memory, agp), then slowly raise voltages if you feel the need for speed- at your own risk of course. there are a lot more experienced people here than myself though regarding overclocking- hope that i've been of some assistance though.
consider adding more case fans- both front and rear of case if possible (increase air flow thus keeping case temps cooler).