I would suggest that you go with the 1 GHz @ 266 MHz bus. The higher bus speed, coupled with any sort of overclock you could probably squeeze out of that chip, would be much better for you than the 200 MHz FSB of the slower CPU. I would suggest that you look at a 300W or higher PS, though. I have never run a 1 GHz Tbird with a 250W, but it might want more than that PS can supply if you have anything like a CDRW, DVD, awesome video card, etc.
Hope this helps you!
