I am aware that I need to convert to radius yes. I have indeed tried doing this and the numbers don't look outrageous, but I can't really find much typical values to compare with on google. Most sources simply indicate that the $M^2$ of high-power diodes (such as the ones I am looking at) tend to be "bad" without giving typical numbers. So I guess my real question if whether or not the emitting area of a diode can be considered as being the waste of the (approximately) gaussian beam coming from it?

@MichaelSeifert As I said I'm not too concerned with the actual amount of drag and therefore linear drag should work just fine