I use the 3x6 on most lead (RARE piece) and two 3x4's for some lead. On one of these I bored the vortex of the cup out and opened up to a #16 or so throat. Helps fight the small mouthpiece edge on exposed softer passages. I also have Steve's new 3x5. The others are all antiques.
I like to stick my 4-2 in a flugel horn for church work. I do have an Al Cass flugel piece too but its a bit too deep for a lot of blowing. I believe that all truly huge flugel horn mouthpieces cause the upper register to go flat. Unacceptable on a piece like Mangione's "Feel So Good"