Safdar, silver or white or any other light colours are pretty tricky to play with. They are not meant for depth, they are meant for a smooth and glossy touch. Dark colours are the ones which are preferred even in detailing combinations because they can reflect all of the following, depth, shine, reflections and gloss.
GC on black cars would give a WARM feel, NXT would give it a lot of shine. 26 would give it an even warmer tone, with crazy depth. personally i like 26 over NXT+GC combo, because it gives awesome depth, shine and also protection. I personally like experimenting now, do half side of the car with NXT then the other half with 26 just for the sake of comparison, both waxes are good in their own way, but i like 26 more because some days you want that warmth in your car and that goldenish feel rather than just silvery shine, which comes with NXT.
Plus 26 is from the professional line, there was some person on the detailing thread who said since 26 is from the professional line, sirf 2 din ki chandani hei, i dont like posting in that thread anymore, otherwise i would've challenged him, in fact no, i wouldnt have even replied to such a stupid comment. Anyway the thing is for lighter coloured cars synthetic waxes work great, but the gloss which natural waxes put up on a properly cured paint would drive you crazy.