Well, MooreOn, I think you're at least partly right about the over-long cars. I mean, while the cars on, say, Mean Streak, for instance, also have trouble tracking curves (for the same reason Sonny's trains can't track), the shuffling is far more noticeable on Sonny, and I think that might be because the cars are so long. My point is that even if the cars are shorter, the problem still exists. The problem is minimized as the distance between axles is reduced, but it doesn't go away unless you build the car so that it can track the curve.
As for the question of why all the big wood coasters are twisters...
Personally, I think Shivering Timbers would work just as well if it were 200' tall, but larger wheels would probably be a necessity. I wonder if the lack of huge out and back wood coasters has anything to do with available real estate. I mean, Shivering Timbers is not only long and tall, it is also quite wide to support the lift hill. Perhaps to be practical, an out-and-back 'hyperwoodie' would require a steel structure, not because the wood structures can't be built that high (Son of Beast proves they can) but because a slender steel structure can fit into a narrower footprint than an equivalent wood structure. I'm guessing that Magnum XL-200 for instance couldn't have been built in that space with a wood structure. It's only a guess, but it seems to make some sense.
I keep hoping some wood coaster train builder will build a train modelled after the Arrow Runaway Train. I think it would work rather well...
--Dave Althoff, Jr.