Oh so ATi is just not doing anything for your 4870X2 & your friends 4870X2, ATi must of singled just you 2 out.
There has been fixes for the 4xxx series since 10.5 & even seen improvements on my friends 3870 CF setup since 10.5 even though its not specifically stated.

Actually it's common knowledge that driver support for multi GPU's - especially 4870X2 - has been somewhat neglected; seeing several reappearing bugs in the releases through the last year or so.
Well debated over at Rage3d.
Not to sound supercilious