I have also been looking into this recently as about to start my IMC training. I have got RANT and was planning on getting the Elite Pilot Core thing as couple of people at my club recommended it. I see its got some bad press above from Bose-x who always seems to give good advice so maybe i'll have a rethink!
My computer is not very fancy though and i thought it might not cope with FSX to well?
Cheers