Although you probably can get used to a fair range of things, there are a couple of competing issues at play here:
1) Playability - if the strings are too close together, your fingers can have a tough time being precise enough to play well. This is not a single dimension issue - string spacing is at work both for your plucking and fretting hands. I have huge hands, and this is an issue for me - more in my fretting hand than in my plucking hand, though it was a bit of an issue both places.
2) Overall width and reach. Again, this is a factor for both hands. If you play a wide spaced 5 (or 6), the neck can get really wide, and the reach for the highest string can be an issue with your plucking hand. A lot of folks have to develop a floating thumb to play a 5 or 6 well. In my case, I didn't go that route - my hands are fine (they're huge) with a 5'er at 17.5 mm spacing. I'm also fine with a 1 7/8 nut width, though both of those are probably pushing things - I'm not sure that I'd be OK with a 19mm spaced 5'er at the bridge end of things, because of overall reach.