Just offering an opinion here - I have bikes with varying stem lengths and top tubes - I've substituted longer for shorter on several of those with shorter TTs, to avoid riding like a scared cat :
(That gets very uncomfortable on long rides)
My sense of the before and after condition is that while I can stretch out a little more, the ride handling/stability is unaffected. (-Which would make sense, considering that the caster and the trail is established by the angle of the steerer tube, and the distance to the tire's contact patch with the pavement respectively.)