
A map that's 50 mb? Is it a whole campaign or just one map?
I have around 50+ custom units along with icons and custom sound in my map and it's still only 4.3 mb ish. The 100 kb models that archive to 10 kb ftw (a lot of Bob's models). I would really recommend getting into the habit of limiting map size. When I started my map, i could care less and now I'm slowly starting to replace them.
When a map is too big, it discourages people from downloading them. If I remember correctly, even the high quality Diablo III RPG is 5 mb.