I'm using a Durst L1200 w/150mm Schneider lens and I've been doing prints up to 12x16 from 4x5" negatives. I've been wanting to try some 20x24" prints to see how they look, but when I max out the adjustments on the Durst I can get the projection size to be about 18x22". The head is not all the way at the top of the column, but I've reached the limit of focus.
I also have an 80mm lens, but nothing in between. What's the best approach (other than leaving a 1" border around the print, which actually might be a good thing!)?