I like the idea of a very slow shrink down to mid 3' range. I'm 5'1 now, so going down to 5' isn't that big of a deal. I love imagining a woman having to finagle the countertops though, discovering how weird the world looks, simple things like brushing her teeth or using her keyboard.
Plus, I think mid 3' is the absolute smallest you could go and enjoy a good sexual encounter without being split in half.
There's a reason the Medallion story by Nomdreserv is my alltime favorite SW story. Slow enough to enjoy all the heights and it stops at a still functional but fun size.
Edit: Oh hey, I finally delurked.