Thanks for input. You confirmed my concerns that an efis is not as capable as my 740 for navigation. Please elaborate on how ifly is different than efis .
Larry,
The iFly is a very capable Electronic Flight Book (EFB), basically, what handheld GPS's have morphed in to. It gives you all sorts of position information, navigation, and charts, plates, etc. A very good tool to have, especially if you move between airplanes - you always have something familiar. I use ForeFlight on an iPad for this same function - many ways to do it.
An EFIS is a built-in Electronic Flight Information System - part of the wired in avionics of the aircraft. it will replace all of your primary flight instruments, including those with air data (pitot and static). In addition, it will interface with your engine and fuel system, so it can give you much broader navigation insites - like how much fuel you'll have at the current flow rate at each waypoint in your flight plan. Advanced systems will interface with radios, transponders, IFR Navigators, etc. An EFIS is an entire instrument panel...and more. Most full-featured EFIS's today will give you all of the navigation capability of a portable EFB, plus realtime interface to the aircraft.
Asking if you need an iFly or an EFIS is sort of like asking if you like airplanes or bananas - they are two different things. If you are going VFR, and have a set of air data plus engine instruments already, then the iFly will be a great navigator. If you are looking for teh iFly to be your entire panel - it is missing many key elements.