Never read the books. Best friend (who's a girl) made me watch the damned thing with her tho (as my gf refuses to watch it cuz she thinks it's stupid), thus I'm not aware of any book "feats" the Cullens might have. I'm feeling that a lot from the pro-Twilight side read the book and based their position on how the book described the fights rather than how the movie portrayed it.
Thing is, speed-wise, from what I saw in the movie, is that they're fast (Spiderman movie fast, maybe), but not untouchable. Certainly not Flash-fast and certainly not too fast for Hulk (who had a few speed showings in the movie like catching a newly ejected seat) or Thor (who had a few himself, including dodging a thrown aircraft wing at close range while running towards it). The fight with Felix had a few blur-moments but that was not all too impressive as well as their movements looked fast but they didn't really look like they were able to fit that many movements within the time frame they did it in (looks like a backflip, body slam attempt, countered by a double frontflip, countered by a successful chokeslam then a standing kimura reversed into a hammerlock attempt w/c was avoided and countered into another hammerlock attempt w/c Edward rolled out of w/c made him walk into a front choke then a slam using Edward's neck into the stairs just with a lot of blurry camera play). I dunno, just my opinion. /shrug
And as for their skin being "harder than surgical steel", when was this mentioned? I recall it being mentioned than a scalpel wouldn't cut their skin, but never that it was harder than the metal itself. Certainly not SHOWN in the movies as we've seen Edward cracked Riley's skull when he rammed it against a rock (rock didn't break and the impact didn't ). And Edward was getting reamed pretty badly in New Moon with their fight doing SOME collateral damage in the surroundings but nowhere near the same ballpark as what Thor vs Hulk (or even when Hulk was chasing the Black Widow) did. I mean Felix chokeslamming Edward to the ground (w/c, the force of the impact cracked Edward's skin) only cracked the marble below them, not very impressive at all.