Wheel width question

I plan on using M/T 235/60-15 ET street tires to drag race as I also have to drive the car to the track. Rear suspension is stock dimensions. The recommended wheel widths are 6 1/2" minimum to 8 1/2" maximum.

The wheels I want to run come in widths of 6", 7", or 8"...but not 7 1/2". Should I go with the 7" wide wheels or the 8" wide?

The car in question is '73 Duster. Sorry for the omission.

Thanks!