A 100 mhz graphics or front side bus over-clock wouldn't hurt anything. Also I do not know any efi commands.
Most of relatively new Intel processors, which are not aimed at overclocking,
could still be overclocked - but with limitations.
Desktop CPU example:
while i5-2500 (non K) is clearly not for overclocking, the CPU Multiplier can
be increased by 4 bins, increasing the frequency from 3.3 GHz to 3.7 GHz.
Similar story with mobile CPUs. Basically, if you look on this problem closer, you could see that
all this is essentially the same as forcing your CPU to go into Turbo mode and stay there.
By doing that, you are not forcing the CPU to work in some custom mode - which is not approved by Intel;
instead, you are forcing it to go into Turbo mode and stay in Turbo mode - which IS approved by Intel.
So, that is not exactly overclocking. But result is the same - your computer runs faster!
EDIT: The only problem is, how to get it working?
You are probably right: by discovering a set of awesome EFI commands which allow to do that.
I could also think of some other ways, but they are much more complex.