I think good hand position/bass position can make hand size nearly moot. There are guys with hands that may not be small, but they're playing 8-string and 9-string ERBs and still able to reach every string with every finger up to the 12th fret. I have a 7-string bass with 18mm spacing at the bridge, and I can reach across to the B string with my pinky up to about the 17th fret at speed. Well, maybe I tip the bass down a bit...
Conversely, I've seen people with horrible "Boston Strangler" technique, who've become accustomed to actually "fingering" the E string with their thumb. For these folks, even a 5-string is impossible (and on skinny-neck 4s, they rarely venture above the 6th fret).
The moral is pretty simple: Good technique will allow you to play a 6-string bass all over the neck with very small hands, while bad technique will limit you even with the smallest 4-string neck and gorilla hands. Look at little Wanda in post #7 above. No question she could reach a couple more strings if she had them.