I got my slide back from my gunsmith today and he was able to successfully remove the sheared screw. He said due to the McMaster hardware being heat treated it was pretty difficult to extract. I asked him to chase all of the threads and now the hardware threads smoothly and easily, no hint of resistance.
I'm probably going to take my second gun to the gunsmith and have him chase those threads as well. I see a big advantage using the McMaster hardware due to the added length and torx head so I'm glad to get this sorted out.