Could have to do with the tint of the windows, lightbar etc. Bugs has his way of making his, probably with brighter light textures, as with EVI, he uses more darker textures.
I think I have a pretty good computer, but you could have the best of computers and the game will still run slow with enough mods installed. As it's just a console port, that's the way she goes. Hopefully they'll put more work into the PC Port for GTA:V.