Unless you're regularly at the top end of fourth gear on tightening radius, off camber sweepers with one and a half turns of opposite lock wound on to counteract lift off oversteer then I don't think you'll notice the extra weight of the sunroof. I love your ideology
though.
What you may notice (slightly) is a small loss in torsional rigidity as there is a bloomin' great hole where there used to be solid metal. The Mini has a very stiff chassis which shrugs most of this off though.
As far as weight is concerned then unless you are trackdaying on a regular basis then the 60lb won't matter either. I guess it depends how obsessive you want to be concerning ultimate performance, were talking fractions here. You'd be as well off wearing shorts and a vest, leaving your small change at home, removing the headrests, floormats and parcel shelf and keeping your hair short, that should save you a good couple of seconds on the school run. Once again, my type of guy, I wish you well.
