Okay, so i have been searching the net and some Russian sites. Knowing how Russians love to make BIG stuff i wasn't surprised in finding a hammer editor modification that supports a 32000 x 32000 x 32000 units map!
https://sites.google.com/site/gshltools/mapping-tools
I have only tested the length of the map. I have created an RMF which is in 9300 units from center long.
At first, my CS could not go over 8196 units from center all thou it rendered the block behind it. There was some kind of an invisible wall blocking me, plus the spray logos i did on distance >4096 from the center appeared in the center! Must be some engine bug due to map being over limit.
After that i have tried it in half life by replacing the delta.lst. Half life allowed me to go all the way to the block.
So im guessing with out modification of delta.lst half life can safely go up to 16000 x 16000 x 16000. But more wont allow the player to pass, could maybe be used as scenery area? I dunno.
So im posting this here for you people to see and test.