As far as my Schneider Literature indicates, they never made a "HM" high magnification lens in the 300mm focal length (unlike Rodenstock). So 2 to 20x is it.

My 300mm is a Rodenstock (non-G) and my 360mm is a Componon (non-S) so I cannot give you any first-hand information about the 300mm Componon-S. My guess is that it will be just fine for your purposes. (B&W enlarging , right?)

Do you have a lens yet? Here is a Componon-S 300mm for $100:

The only reason I have not bought that lens is that I already have four lenses for 8x10 enlarging and they pretty much do the same thing.