tire size & gear ratio

id like to know what size tires (26-28") and rear gears everyone is using. what kinda rpms does it run at say 60 mph?
i trying to decide between 26 or 28" tires. im running a 4 spd and a 391 rear. im thinking 26" (295 50 15) may be too small but 28"(325 50 15) i may have clearance issues. what do you think?
btw these are 10" outlaws