Hi, KSP may run better in 64 bit mode, but is generally more unstable. This is because KSP is built on the Unity 4 engine, which, currently, is 32 bit. The warning is simply telling you the game is prone to crashing, regardless of mods - almost clockwork. However, if the lag when running 32 bit is Unbearable, and you're comfortable with the regular crashes, then 64 bit is fine. Also, 64 bit Ksp IS 32 bit KSP, just tweaked a little, so versions should still be up to date. Happy rocketeering!