I fly Fixed and Rotary wing and operate an Enstrom 480 helicopter which has just had a full avionics refit (in fact it was completed yesterday). Originally it had a gimball mounted skymap IIIc which I hardly ever used. I just didn't like the screen resolution or the way it displayed features. I much preferred the Garmin 496 (previously I had a 296).
Yesterday, however after viewing my new panel in the hangar, I think I am going to be pleasantly surprised by the new kit which has been fitted. The Skymap IIIc has been replaced by a KMD 150 which is effectiveley the panel mount version. The screen seemed much brighter, but sadly I can't fly the aircraft yet due to another technical issue which is being resolved, so I don't really know how much better it is. I have also panel mounted the Garmin 496 using the panel mount kit and this looks great.
IMHO I would go for the 296 (not the 496) unless spending the extra cash isn't an issue. You will not notice the faster refresh rate, the preloaded VRP's can be loaded manually from a csv file (I have them if you want them) and you can't use the wx feature yet.
If you want any more help just let me know.