The fourth page of the zhome write-up mentioned above has comparisons of the ratios of the various boxes tabulated. The 5-speeds are all pretty similar, including the 71C.
I don't think the box swap needs to be seen as a performance orientated upgrade. More as a reliability and modernity upgrade maybe? They are newer and a stronger, more refined generation. In my case, I decided to go for the swap because I wanted a more modern, tighter shift and had had enough of the looser, quirkier shifting of the current box. It was increasingly irritating me, comparing unfavourably to the shift experience in my DC2 Integra TypeR. I've also opted for a quick shifter kit, which are plentiful for the 71C.