Sure you can OC with fsb, especially with quality ram that you got.
However FSB oc'ing introduces problems like shortened lifespan of PCI devices (you oc them too..) etc.
Unless you don't do radical changes and/or your mobo supports exotic PCI dividers, you'll do fine.
Multiplier unlocking is mainly for those guys who want to ooze the last bit of performance by going to 170+mhz FSB
XP unlocking is a bit of a pain..
Or to the casual dweeb who just taps the multiplier up a couple notches to gain an easy oc (I have factory unlocked 1.4 t-bird..)