Is it ok to use a 7.1 or a 6.3 to fish deep diving crankbaits? Or should I be using something else?

Try them both and see which one works best for you. Some folks like the lower gears for deep cranks because they supposedly don't tire you out as fast. I use whatever rig is handy. I usually carry 6 or 7 rods in the boat and 3 are dedicated to specific lures. The others are open for whatever seems appropriate at the time.