Again, I'm only criticizing your English because some of your posts are quite illegible... no punctuation and very poor grammar.
But as for his needs, yes, I realize none of us know. But I maintain that it doesn't seem worth it to upgrade the B&W. It is however worth it just to purchase the base machine for $100. As it's been said above, he could even just sell the machine for a profit right off the bat.
As for flashing cards... I don't think you've flashed one. Some require jumper adjustments, and others don't even have the right voltage. If you flash and improper card and insert it, you could short circuit your PCI or AGP slot, and even fry your mobo if it's done incorrectly. I'm very wary of flashing, and I prefer not to do it, even if it saves a few $$$.
Also, for all we know, $100 may be all he has to spare at the moment, so upgrading may not even be an option.
As for the bus bottleneck, it's not going to be nearly as significant as the CPU bottleneck. You're talking about a 150 mhz difference on the CPU, and only a 33 mhz difference on the bus. Now, if it was a difference from 167 to 900, for instance from a G4 to a G5, then that's obviously different. But the bottlenecking you "think" will happen between a 66 and 100 mhz bus isn't nearly as significant as you think.
Furthermore, I find it curious how a 16 year old, in England, no less, was able to get a Tiger preview...