Ok, 16 or 17 is very expensive in Brasil.
But in comparsion 14x8 and 15x 7 how is better, I lower the front (Shelby mod) and rear (lowering block), and to improve traction I plan instal Shelby under ride traction bar.
My guide is the Ford muscle article "Get a Grip" and the 15x7 is one good choise.
The 14x8 wheel have 225/60-14 tires and the 15x7 have 205/60-15 225/60-15 and oters.
Considering lower is better the 14x8 will be better than 15x7, the center of gravity still lower.