TritonS

I think if you limit the battery to 50%, the battery will drain at the same rate as normal until it reaches the 50% mark. Effectively you will have 40-60miles of high mpg driving and then the rest will be at a lower mpg. Take this with a pinch of salt as I've only done it a few times haha. It definitely feels nippy on the motorway, plenty of power to overtake in my opinion, especially in sports mode if you need the extra responsiveness.

Similar experience here, when fully charged up and on hybrid mode (on the 'Normal' setting), i get a about 65-75mpg, Depending on driving style/weather that charge lasts me about 80-100miles on the motorway. Once out of charge, I get about 50-53mpg. Of course you can limit your battery usage to a certain percentage if you know you want to save it for a round trip or if you know theres town driving at a certain section.