Larger rotors will displace heat better and you will be able to modulate the brake a little better.Larger rotors will give you more braking leverage(less pull on the lever for the same amount of stopping power). It has nothing to do with stopping power.If you can lock the wheel,that's as good as it get's.

If you want a bigger rotor,go for it.No down side except a tiny bit of weight.The rotor will last longer,stay truer longer and you will have slightly less pull on the brake handle.