Ah, language-baiting. How I miss the days when it was completely clear cut [old-time java can suck my balls], although I notice that the arguments haven't actually changed.
I just want to throw in that comparing C# the language/CLR to Qt is like comparing C to openGL.
For want of an apples-to-apples comparison, it might be wiser to go with "the C# interface to winforms vs Qt". And it's my limited understanding that in that realm, Qt crushes C#/winforms performance. Of course, the case now as it was then is that the glue layer is sufficiently skinny that it's *all* about the other stuff you do rather than the cost of one extra function call.
Also, sixty eight properties is a pretty good approximation of zero in terms of memory needed. I would go so far as to point out that the winforms button is on an equal footing