Ok, I'm trying to get my lighting to be dark and gloomy to match the Grave256 skymap if anyone can give me a good Light_env setting that would match this type of sky it would be greatly appreciated and earn you a mention in the credits!

Someone will certainly give you a light_env that fits your tastes but,
usually mappers work on this kind of things in a small test map.

Plus, without the sky you are referring to, it is obvious that the angle and pitch won't match this sky.

Yeah, cut out small portion of map and try various settings. I don't think that anyone could tell you right values because light_env setting give different effects depending on texture set used.