I'm 6'3 so there is never any room in the back behind me whatver car I've had so far. I've had no complaints from the people that I have had in the back on the passender side though.
It's good that the rear windows drop so you can reach over the bodywork whereas the e92 has fixed windows.
I've not had any issues with leaks so far but I've not had the car long. Typically it did rain for 3 weeks solid when I bought it though and the car remained dry inside.
I've not measured my car but I have found these images showing the size difference between the two cars e92 on the top
It's a difference of 83mm between the two so not a lot.