Both of those add power along most of the range, really... Superchargers are in limbo right now, as there aren't any production units for the car, but those help off the line, too.
A small sized turbo will spool early enough for most anyone to be happy with the low end; It won't make a huge difference 'till boost builds though. I plan on using a Mitsubishi-style T25 turbo, and most of the kits around here use T03's, or similarly sized turbos. GT28's, too, from time to time. The T25 boosts in really early, from what I gather, and will load up all the way pretty quickly. That's enough of a gain for me, as I'll probably only run 8 or so PSI, at most, depending if I go with an FMU or an EMS for fuel, but that's a whole different story; I'm custom making my setup. =)