We finish ours a bit on the lean side to maintain our "lean beef" claim. Our customers are opposed to paying by the pound for fat. Trick is to feed enough to produce the IM fat (marbling)
without the excess back and kph fat. We go by age and time on grain....start the steers gradually on cracked corn 120 days out and increase to 15lbs corn/10-15lbs alfalfa during the last three weeks of finishing. We have had good success using this method. We did hold one Hereford steer back from the fall production because he didn't gain like his peers....he made the rotation this past weekend, a bit on the small side but just the right amount of fat.
It's a judgement call...how long do you want to feed him...for your freezer I'd fatten him up...it's your animal and you can always trim the carcass.
Good luck...you'll not go back to store meat again.
DMc