Back in the day, my
FLGS used to be in a store little bigger than a closet. As such, in order to get 4 tables in the space, they couldn't be bigger than 4x4 foot. I only rarely played above a thousand points then, but at that points level a 4x4 table felt just fine. I even used basilisks then and never had to worry too badly about the minimum range thing.
I think you could probably stretch it to 1250 without too much bother, but 1500 might get iffy, just because a horde army is going to have a hard time fitting everything in there (without shenannigans like al'rahem). That said, I played 1500 at that with non-horde armies and there was still enough space. Higher than that, though, and I'd say you really need the extra two feet of width.
If you want to see how 1,000 point games play out on that table size, click
here (starting at game 22).