The thread you mention still won't say what the fastest 8GB MS Pro Duo is though. Instead people agree 2 4GB cards are the better option.
As stated in that thrwad too, personally I prefer one 8GB MS Pro Duo so I won't have to take it out. From what I've seen so far, the SanDisk 8GB Extreme III's are the fastest 8GB's atm, but they're very expensive ($125/€100).
SanDisk 4GB Ultra II's are more affordable, but I'm unsure if the lower speeds compared to fast 4GB ones is gonna make a real difference in gameplay.