I know that the default values for this is 66/33/100, and I am wondering what will happen if I change it. I think nothing should be done to the SRC, but how about the other 2 values? Say... 80/40/100? What would happen?

That's a huge change and it probably won't post, let alone boot. Do you know how to reset cmos (jumper or battery removal) before trying it?

I know how to do it, but if you say it won't post, I won't bother.

Everything I've read and done with OC'ing my system has me locking the agp\pci to 66/33 and run quite stabley while clocking everything else.

How far have you taken it?

I didn't touch it. Can't be bothered resetting Cmos and all that. I've been advised strongly against changing those settings.