Maple FPS - kMS vs gMS (OMFG)

If the clients are all the same, how come I never experience any lags with JMS? (except at 2 to 3 AM local time where the game is glitchy)

The client's aren't all the same. Though all the clients (except for KMS) are only compatible with XP, each branch has done their own thing to the client to suit the needs of their region. GMS is probably one of the most hacker infested version out of all of the versions, so in response, Nexon America probably has to do some pretty hackish workarounds to get those hacks patched.