They do all right as long as they are new or near new condition,if you put on the 3" system put on the SCH EASY CUT SYSTEM AllOT OF GUYS ARE PUTTING IT ON I DID lAST YEAR AND HAPPY WIYH IT.
nothing wrong with 1.5 if used in right place.1.5 sections ,if one tip breaks you can keep cutting, 3 you stop and change section. 1.5 should not run over 400 cpm. 3 need 500. if in no till with stalks sticking up definately needs 3. cnh 1.5 section knife will jump rock in, the knife tip is out further than the guard.
Had the 1.5 on a NH 973 head once and it cut good in 30" conventional beans but I started doing no till and I did not like them at all. Changed to the 3" ones and they do a much better job in no till beans that was planted in corn ground. 1.5" will push the stocks and leave a bean plant there. You will not see it that day but come back a few days later and the field don't look to good then, all them beans sticking back up. Go with the SCH system. That looks like the best out there. Ilnh