I'm looking at options for clear coating CF+epoxy panels and was wondering what the difference is between a clear coat like Duratec Sunshield and more economical automotive clear coat sprays (like EW 2K High Gloss Aerosol)? 

Duratec also offers no UV protection, despite its branding. Ive tested this thoroughly, and concluded that parts are almost better off as raw epoxy than coated with Duratec. They will suffer from UV exposure quicker with Duratec on them (obviously this is true of the epoxy I am using, some epoxies are more sensitive than others). The benefit is that the Duratec can be sanded back and polished again, so you can restore the finish whereas raw epoxy will be ruined.

The best is to do as Fasta suggested, coat with Duratec to avoid any pinholing issues, then report with a top quality automotive 2k for UV protection. Obviously this is the most expensive and the most labour intensive route.