About 10 or so years ago I designed and fabricated a touring frame. The fit is the same as my road bike, but the chain stays are 47cm instead of 42.5cm. There are some real differences between them when ridden. The touring rig steers wide, and is unable to be slammed into corners. Of course it is not ridden that way because it is a touring bike. The shorter chain stay bike is much better at slamming corners. It also feels more alive when sprinting and climbing, which it should.
One thing I didn't expect when I made the frame was absolutely how comfortable it rides on rough stuff. It really is amazing and is tied for favorite bike with the other bike I designed and fabricated (the 42.5cm chain stay bike). I also have a 1985 Miyata 1000 touring bike and it has 45cm chain stays. This bike is more neutral in cornering and does not swing wide like the 47cm stay bike.
As for high speed mountain descents, if the bike fits well and has the right tubing for the job, it will behave nicely regardless of the wheelbase. One thing to note is if you have a very upright body position, high speed descents may be a bit nervous because of the weight imbalance between the axles.
Oh, one more thing, BB height. Don't bother with the nuances of it because 1cm of difference means nothing in real terms. I use it to adjust stand over clearance when I design a frame.