What is the rpm sweet spot for highway driving

I enjoyed reading through all the comments and the discussion. I had 2.76 and it seemed sluggish. I have 2.94 in it now and I can tell a "seat in the pants" difference. I'll probably try the 3.23 but, I'm pretty sure the 3.91 is going to be too much. I don't have a tach and the figures are calculated. I don't drive highway everyday but, when I do, I'm running 70-75. Maybe that's too much for an old car. #-o I really don't care about gas mileage, I just didn't want to cause undue wear and tear on the 318. I may need to rethink the low gear trans or stall for take off. I'm probably not appreciating the quickness of the teen. I'm going to let all this roll around in my noggin. Thanks Craig