bose-x
OK so not a factory option, what I was trying to get a grip on is what the C172 can do as a production aircraft.
We can all fit aftermarket bits of kit but I suspect that the tank you have is a ferry tank that is only cleared for ferrying the aircraft, not as in the case of the Robin suplimental tank that is a standard factory option.
I have no objection to Cessna aircraft they are a very workmanlike And rugged bit of kit (I own two of them) but in pure performance terms the fact is that the 172XP is out classed by an aircraft built out of something that looks like old tea chests with a fixed pitch prop and 20HP less power in the engine department.
As me if the Robin is a realistic rental aircraft and I will tell you that I would take the Cessna each tme!