I think turbo means the walk speed is greater....but I could and probably am wrong. Ask Fearon, he would know. I just play on the servers, not run them! 
No turbo is the instant switch...Original gungame plays out that you play a round get a kill, and you get the next weapon. Turbo enabled gives you the next weapon automatically so you can gain multi weapons on a single round. you also have knife pro where you steal player levels and bump ppl back a level when u get a knife kill. Think that pretty much covers it. Mark should be able to load up GG if we'd want to do that on source (thats all my CS:S server runs 24/7 now)...I think the latest version they have is GG4 (es_load gungame4) but I havent checked forever so they may have something newer. Mark should already have mani and meta installed because of zombie so it would be a simple add and config (can give the configs I have if you'd like them). Biggest prob would be that gungame works best on GG maps..I'll list some I think are sweet. These are a few of my fav of the 50 I have on the cycle list
gg_pool_day_gx
gg_churches_x_final_fixed
gg_tetris_v3
angry_overpass
gg_minesweeper
gg_spongebob
gg_lego_arena_2
gg_simpsons_32
gg_lego_arena
gg_simpsons_burg
**Also I have CS:S configured (not running on this one but the other) on the same as the BF2 and CoD4 server so if I would bring the server along for BF2, I could launch a GG CS as well off it (only prob would be that it does a redirect to my webserver hosted by godaddy for uber 700KBS map downloads...we'd have to setup a network redirect so those who dont have the maps could pull them on the fly..some maps your looking at about 25-35MB and the last thing we'd want would be to put stress on the server by having ppl dl maps while others are trying to play the game and lag out at 100 pings on a lan connection..LOL)