In short the 12 will be slower at the same RPM but more torque Best bet would be to go to EC website. Click on "Technical Info" toward the top in blue writing on the home page. Then click on EC Distributing Mower Speed Calculator. You will need your tire circumference. For me this is easier and let's me see different combos and you can adjust your RPMs up or down. Just remember more speed less torque more torque less speed. Hope this helps.
Sent from my iPhone using Tapatalk