I did some testing of my 45MX as I set it up. It seems the largest size enlargement I can get with 35mm and a 50mm lens is about 16 x 20.
20 x 20 with 6x6 and a 90mm lens. I am using an Aristo cold light head...

Does this sound right and if not, where can I find out this information?

Also, I had to manually guess the head distance by looking at the instructions as the negative size indicator is missing, so I am going to have to locate or fabricate one of those now.