hmm, let me see if I can lay a bit of tech background in here.
Generically, there are three things that affect how the pedal feels to the driver, and how "responsive" the brakes feel.
First is pedal travel, ie how far the pedal goes when you push on it.
Second is pedal force, ie how hard you have to push on the pedal
Third is brake torque, or braking force, effectively how much the car slows down.
Each of these is closely related, and the combination of the three at any given time determines how "responsive" the brakes seem to be. Brake engineers try to design the system so that all three build evenly so the system feels confident, and controllable, but not "grabby", or "mushy", or just plain scary.
As an example, a brake system with low travel, low pedal force, but very high brake force will feel very "grabby" ie it doesn't take much on the pedal to make the car slow down a lot.
But, if you have a system with lots of travel, low pedal force, and normal braking force, the pedal will feel soft and mushy.
Then, if you have a system with low travel, high pedal force, and very low braking force, that will feel downright scary, because you would push hard on the pedal and it barely moves and the car doesn't slow down . . .
In a race car, most drivers like a pedal with fairly low travel, and a bit higher force, and of course excellent brake force. This results in a pedal that feels firm, and doesn't travel a long way, but of course has excellent braking force. This allows the driver to use pedal force mostly as a way to very precisely modulate the braking force.
For me, the stock contour SVT brakes are slightly on the soft side (I'm biased, I like race car feeling brakes . . .) but otherwise very well balanced. When you start to change components, you change the characteristics of the system.
First, the warmonger kit, because it changes the least. Since warmonger's kit only changes the rotor radius (ie larger rotors) and the rest of the system stays the same, the only part of the three factors that changes is the effectiveness goes up. So that means that while pedal force and travel are still the same, the effectiveness goes up, so when you press on the pedal, the same old press on the pedal results on more braking force. ie, it feels a little bit more "grabby".
The difference w/ the full Focus SVT setup, is that not only does the effectiveness go up with the larger diameter rotor, but the pedal travel gets a little longer also, because the Focus SVT caliper uses a larger piston, which means you have to move more brake fluid. So, now, compared to stock, the pedal travel gets a little longer AND the brake effectiveness goes up. So you get a combination of a little more mushy AND a little more grabby.
Honestly, neither is a severe change, and most drivers will just be happy to have the extra braking effectiveness. For me, typically I would choose the warmonger/NPG kit, because I prefer a firmer pedal no matter what; but, if I were in a situaiton where I needed brand new calipers anyway, then I'd consider the whole FSVT kit.
Fwiw, I'd still run either a warmonger rear kit, or the TCE rear kit when upgrading the fronts as well to keep the brake bias in line. While it is true that the front brakes do most of the work, the rear brakes do have a big effect in a number of ways. Keeping the natural bias relatively close to the stock bias is very desirable. Maybe I'll run through some of the tech behind that one of these days when I have time.