Just going on what I've been reading.
same size piston in the master pushes XX amount of fluid. Since the pistons in the 2500 calipers are a good deal bigger, it's going to take more fluid to move them the same distance as the smaller 1500 ones.
In theory, you'll have to use more of the stroke of the master cylinder to stop the same.
But from my understanding the NBS master which is a pretty simple bolt on, increases the MC piston by .2"
Absolutely, it's only common sense. Bigger bore equals more fluid capacity equals more pedal travel. The larger bore will also deliver greater brake pressure for the same pressure at the pedal. So, assuming you have enough travel available you end up with greater brake pad pressure. But, is that a good thing? Good brakes is about far more than just "locking them up". Best braking is acheived with around 10% wheel skid. In other words, you're doing 50 mph and the wheels are rotating at 45 mph. That's what ABS is trying to acheive in a perfect world. Your front brakes should skid just prior to the rears. That keeps you stable and achieves best possible braking. Improve the fronts too much and they'll skid too long before the rears. As Sparg93 points out, that will increase your braking distance.
Putting in an NBS master will make things even worse. The NBS master is designed for four wheel disc. Using it with disc/drum setups may improve feel, but at the cost of increased braking distance.
Brakes act as a system. Improving one part of the system without understanding what you are doing will only decrease performance. I'm not saying brakes can't be improved; they can. But you have to change the whole system. The easiest way to do this is to match all brake components to a factory system. The ABS, master cylinder, combination valve, boost, front and rear brake components all have to match. Upgrading to JB6 brakes if you have JB5 brakes is pretty easy. Just the rear brakes and combination valve need to be changed. If that isn't enough, adding hydroboost to JB6 brakes should be more than enough for any half ton out there.
Whatever you do, either match a factory brake system completely or leave it stock. Unless you have the expertise to design and balance a custom brake system.