I agree with 26's being the cut off point for a stock 300 , my 300 spins 26x12 rear and 10 front Mudzilla's no problem , but I do have a cam and CDI in it , my other 300 has 27 Swamp Lites on it right now but it has a 54% reduction , I am going up to something around 30's on it and Outlaw 2's are my first choice
like Mac said about floor boards and tying the fenders up , add a 2 inch lift kit you can put 27's and made 28's under it , but it is going to choke it down hard