Thought that might be the case, but I tried opening up lots of programs at once, so the CPU maxed out (see pic in next post) and the multiplier didn't change at all.
Another symptom is that the windows experience index dropped to 4.5 for the T8300 CPU. The original T7100's score was 4.8.
I was hoping I wouldn't have to try a OS rebuild but I think I'll have to give that a go. Strange though, that even the BIOS doesn't recognise the correct multiplier.