I went to the Hustler web sight and printed out the specs on the Super Z. They are as follows for blade tip speeds. 52 in: 18,900 fpm 60 in: 18,350 fpm 72 in: 18,800 fpm I can understand why the 60 " would be less than the 52" , but why is the 72" faster than the 60"? I,m considering a Super Z with the 60" deck, but I also want maximum blade tip speed for the better cut. Which engine is used to figure these speeds?