The 9800Pro and 5900U are not the same thing...therefore it isn't logical to presume that the 9800Pro would flicker just like the 5900U simply because it is in the same physical system. Whatever in the system (power, shielding, etc, etc) affects the 5900U may not necessarily be what affects the 9800Pro.
And so ladies and gentlemen of the jury...this leaves no other conclusion than that the FX line of cards are DUDS. If you pay a zqillion $$ for high end gear you expect 'high end gear'.
We rest our case.