When I got my Woodland Mills WC88, a mate who was familiar with the WC68 couldn't understand initially why I didn't have problems with the outlet shute jamming up with material. Then when he saw that it was belt drive, and not direct drive, he understood - the flywheel speed on the WC68 is 540rpm (same as PTO speed), whereas the belt driven flywheel on the WC88 spins at 1100rpm = MUCH more airflow!
The recommended PTO hp for the Wc68 is 18 to 50, and for the WC88 is 30 to 100.
The take-home is that IF you have the hp, the WC88 will clog a lot less.