For my very first show, I used only Pro-tan (6 coats!) and I was still one of the palest competitors onstage (I'm very pale naturally anyway). I know some other competitors rely only on Dreamtan the day of the show. It does indeed give a deeper, much darker color, but never fully dries, which can be a bit unsettling the first time you try it.
What I eventually found gave me the best color is a combination of the two. My current approach is to use 3 coats of Pro-Tan the day before a contest (it 'sets' in, darkening over time), followed by the application of 1 coat of DreamTan the morning of the actual show (and a quick spritz of Pam cooking spray for sheen of course!)
Cat, and I know Thoughts1053 and a few other competitors have made use of Spray tan services offered at contests or from private services the day before. For me, I always feel better knowing everything is taken care of and that i don't have to worry about someone else for touch-ups or bank on how their choice of actual 'color' (paint) will look under the lights onstage.