...The 1100, of course<G>
That doesn't mean the 1100/100 system is faster than the 1000/133 would be, because system performance is dependent upon the subsystems and how good a job the mobo manufacturer did with layout and implementation. Were this not the case, all the benchmarks for mobos with a certain chipset would be identical at Anand's, at Tom's, and everywhere else, irrespective of manufacturer.
Yes, the 133a is backwards compatible with 100Mhz...