do you have amd's cool 'n quiet on? in windows power mgmt set it to desktop - max performance/power. your cpu may be throttling when needed to save energy/pwoer when not needed. do that then go back to cpu-z and you should see your 16x multiplier.
Cool n Quiet is useful, but when you're trying to OC it actually slows you down. Try booting up or using applications when it's on and then when it's off. There's a noticeable difference when it's turned off, even during idle.