first, i have to say i don't have any ddr boards yet, so what i am going to say is just what i think / believe.
i don't think the reason why fsb o/c difficulty is due to the amd processors. from what i learned, early on amd has stated that their chips are well capable of running 133 fsb. the reason is the chipset and the ev6 bus, which doesn't run high fsb well. the chip (tbird and duron) are very well against 133 fsb
i have heard both ways that the 760 chipset does / doesn't run 200mhz chip. i think it should, reason being you can use pc1600 ddr memory on the 760 board. if the chip you put onto the board can only run at 133, it would be weird to put in a pc1600 ddr which actually runs at 100mhz. i think there should be a setting on the 760 board that choose either 100 / 133 amd chips. maybe not in the amd reference board yet, though...