It'll depend on how the Sabertooth character is developed in the film. If done correctly, size won't matter, since Logan's relationship with Creed is extremely complex and enduring, just like Batman and the Joker. In the comics, Wolverine always was always "dimunitive" at 5'3" tall, with a "little man complex," while Creed was far more sophisticated and psychotic than Tyler Mane portrayed him in the first X-Men movie. It appears that there is some kind of familial or genetic relation between Logan and Creed, and that's perhaps what the filmmakers are driving out with the physical similarities (hair color, size, etc.) between the two. In the comics, this has always been hinted at, with Creed telling Logan at one point that he was Logan's father. Turned out to be a lie, but they could be brothers.
Anyway, I think this new film has the potential to be a great trilogy, if not a franchise, covering some really good storylines from the old Wolvering comics of the 1980s and early 1990s, when he took on the Japanese Yakuza and battled the Black Hand on Madripoor, as "Patch."
Somewhere in the attic, I have all those issues.
Sabertooth has usually dominated Wolverine, and the size difference was used to accentuate the point.
From the trailer, Schreiber looked OK, and the transition to mainstream film might be helped with more “real life” characterizations.
No spandex was a good start.