I'd imagine that with the round inserts in there, you would be golden. I notched the framerails on my old GTI and welded a piece of pipe in the cutout so that I could slam the car and not rub the axels and I never had any issues. Sort of the same theory, round (or half round) cutout in what is essentially a hollow tube (toptube/ framerail), braced with welded pipe. I'd guess that there was a lot more stress on the car than the top tube of a bike.