Funnily enough I had just logged on to post the same question.
In my company we are told to use the OFP as that is computed to a higher degree than the FMS.
However with our new EFB software upgrade we are getting a program called Altitools? I think that's what they call it... But anyway this will do real time processing and suggest re-routes or levels to get in / keep out of the wind.
The theory behind this is the EFB has MUCH more processing power than the FMS.
At the moment I think CityLine have been "playing" with it for a couple of years.