I'm not sure it really matters.

My main bike has 17 inch stays - way longer than usual. 18 inch is touring bike country. The 17 bike has a pretty average front end, 73, average rake etc.

Last summer I was on a borrowed Tesch crit bike, really short and steep all around. Didn't measure the stays but they were at least an inch shorter if not more - that rear tire was snugged right up against the 75 degree seat tube.

Perceived (not measured...) differences between the 2 bikes:
- stomping up a steep hill - the longer stays felt "better" in that the front tire felt more planted, the bike tracked straighter, etc.
- sprinting / accelerating - the Tesch felt much faster, and I did do better in group sprints with it. The back end felt stiffer, but the wheels were different too.

I'll let others get into theoretical stuff.

/ edit: one more thing - cornering. It's hard to say fer sure b/c the 2 bikes have different front end geometry, but. The Tesch (short stays) was great in this one really technical crit I did with lots of tight choppy corners. But at max speed in a sweeper, if you hit a bump, it didn't feel secure/stable - had to really pay attention to stay on top of it.

The longer bike, it doesn't have that instant snappy responsive feel, but in a fast sweeper with rough pavement, it feels really secure - like you're _in_ the bike as opposed to "on" the bike.