What I have read is that the convoy/train movement is a constant within the program, so no matter where the convoy spawn point is, it will take 10 minutes to travel from spawn point to the base town for example. That is why hills have no effect. Until HiTech and crew get around to changing the code that controls those movements, don't count on them being treated as an equal.
So, what has been observed by some of the talented AH map makers, are convoys/trains that have a ground speed of over 500 mph !!!

As far as other issues with GV movement (having to back up a hill in an M3 !!!), and HTC's track record, I believe that HTC will definitely get around to fixing those in the immediate future.