In stating that the groove would make it stiffer I mean that it would be stiffer in comparison to just milling a flat across the end of the bit which is what most shop made ones are like. I would imagine it would add some stiffness where the cutting takes place and would have tendency to guide it more accurately as well. More material can't make it less rigid. There must be a reason that guns drills are made that way. This is only a guess on my part. But it couldn't make it worse at any rate.