Assume 4800 is the top of your operating RPM limit. Adding a blade is load and upping another inch is also load. Couple hundred each would put you back at 4400. Where's the bottom of your operating RPM and when you got your 4800 were you loaded light or heavy. If heavy, and 4400 is within, I'd opt for the 14. If not the 12. Butttt the diameter reduction will give you some relief but will probably nullify the difference in 3-4 if you go with the 14 but the 12 would probably be too light. You can always "control yourself" with the throttle when lightly loaded......If answers fit the question, 14 would be my choice.
