I have had my 700 TBird at 866 just by fsb. {No GFD yet}
I tend to keep it at 816 so the Nic card will work properly.
Temps average 77F, But I do have extra cooling.
My old Classic 750 ran at 940 via mods and fsb it ran about the same
temps. As long as you get a good heatsink/fan combo you should be able to run into the 800s
Daz