How much should 4.10's help me?

The Mach's have a 3.55 stock gear.

With a DOHC car, and plans to stay N/A I would go 4.30's or 4.56's depending on how much highway driving you are doing, how much you drive the car, etc.

If you are planning on a power adder such as a Blower or Turbo you can stick 4.10's or 4.30's