Best wheel size for 4" drop

[68isgreat]

Just finished installing 4" drop springs in the rear of my stepside 68. Right now it has the original 465 4 speed and 4:11 posi gears. I've decided to ditch the 6 banger and go either small block or ls swap, depending on what I can afford. Regarding wheels, what would be the optimum tire/wheel size with a 4" drop that would help me not turn too many rpms at highway speeds, and not rub or stick out past the fenders? I would like them tucked in nice and tight. I also know someone with a set of 3:08 gears that I can get, so that may be an option also.