I have 3320 with 7-iron 72 Inch MMM. LOVE IT!! Never had any bogging down issues. I also have a 2320 with a 54 Inch MMM and with the same grass I cut with the 3320, I would stall the 2320 out quite frequently. I am very happy with my 72 In on the 3320.
Mine is the same., 3320 cab, 7-iron, 72" MMM, cab, air and all the extras. Never bogged down and only wish it had a bigger deck. Don't know why your dealer told you this, but a 60" will only disapoint you.