All the tests done by the usual guys on the detailing forum say there's nothing in it, or the Collinite is a little more durable. The Gtechniq does give marginally better beading, but not really worth the extra cost and hassle.

A few people have used C3 over 476, which is a bit extreme, but should be the ultimate in protection.

As for 476 vs 915. 915 is a little more bling, but a little less durable. In both places it's pretty marginal for me and whilst 476 isn't really designed for show, to me it still gives a good finish and excellent beading.

For a £15 wax it's still unbeatable.