All of these battle predictions sound nice, but expect the unexpected...
The only reason everyone was 99% sure Gray was gonna fight Rufus was because, well, he said it would be his responsibility to defeat him.
After that, I wouldn't be totally surprised if we saw a couple of "anomalies" take on the bigger foes.
I would be pleased, rather, if instead of Gajeel fighting Rogue, JUVIA took on the Shadow Dragon. :)