I have a Duron 650 and am running at 900 also...well done!
you won`t have any problems at all at 900....but dont count on going any higher using the multipliers. my system boots and loads windows, but hangs at 950, so FSB is the only option now.
I am very lucky...I am using a crappy silver orb to cool and my temps are 34 c idle, 46c full load, so that isnt great, but not too bad.
........now if only i had gotten that kt133a chipset.....hmmmmmmmm