Normal T cut, the stuff in the red bottle, is only suitable for solid unlacqured colours, cellulose paint basically. It contains ammonia which creates a cloudy effect on clearcoats. Metallic t cut has no ammonia, but I don't use it, so can't really comment on how good or bad it is. If the paint is quite good, go for the clay bar, then a good wax, if it's really bad, I would normally machine mop it with fine cutting compound, G10?, then polish and wax. I'm no expert, so i'm not saying it's the right way, but it's the way I do it