Re: duratec high gloss or wax for gelcoat?
Personally I use it on all of my larger spray jobs. For smaller stuff sometimes it makes sense, other situations I prefer to use unwaxed gel and pva. The reason I like it is that it is a reactive thinner (becomes part of the gelcoat) rather than an evaporative thinner (which can sometimes break down the protective qualities of gelcoat). If the person spraying knows what they are doing it's a horse a piece IMO. But for someone that has never sprayed gel before I strongly recommend using the additive; it just makes things a little more "user friendly".
Been using it for years and have never had a problem with pre-mature oxidation, fading, etc... BUT, make sure to mix it a little hotter than normal gel. Gelcoat w/out the additive should be catalyzed 1 to 1.5% with Mek-P, if you use the additive make sure to catalyze a full 2% and work with spraying smaller batches to avoid cooking your gun
Hope this helps!
~BWT