Rear Gear Ratio

[Nikotrans]

I'm doing a build on 1957 Chevy stepside short bed. I have a URE 450 HP 383 engine ordered and was looking at a TKO 600 5 speed tranny:

First Gear Ratio: 2.87:1
Second Gear Ratio: 1.89:1
Third Gear Ratio: 1.28:1
Fourth Gear Ratio: 1.00:1
Fifth Gear Ratio: 0.64:1

I was considering 18 - 20 inch wheels.

My question is what would be a good rear end ratio for good performance and decent gas mileage?

Thanks in advance.