What is the rpm sweet spot for highway driving

I would say 3.2 is bit too much for 70 mph, i have that and its about 3000rpm.
I would personally want to get od someday 2000-2500 rpm would be good for cruising. Thats why i drive 55-60 mph most of the time.

If your cam is not too big engine should have plenty of torque to cruise at low rpm


New cars that have 200 hp can easily cruise at 1000rpm 70 mph, so nice 318 should easily do 2000 rpm