Upgrading to 11.75” discs on the front?
You are just asking a simple math question. 1.75 squared x 2 is 6.12. 2.75 squared is 7.56. The factory 2.75 caliper has 24% more braking force than the Wilwood four piston caliper. Swapping the Wilwood calipers on your car will reduce braking force significantly. As in, you'll feel the difference and you won't like it.
It really
isn’t that simple. Yes, the 2.75” piston factory caliper has more piston area than those 4x 1.75” piston wilwood calipers. And let's get the math right. The 2.75" caliper has a piston area of 5.94 square inches. The 4 piston wilwoods come in at 4.81 square inches (only 2 of the 4 count for the math). A Viper caliper, which is also a fixed 4 piston caliper with 40 and 44mm pistons, only comes in at 4.30 square inches of piston area.
But the math assumes 0 losses, 100% efficiency. No leakage past the seal, no piston tilt in the bore, no caliper flex, no friction on the sliders, equal pressure all the way across the brake pads, etc. Which isn’t real world. And the single piston sliders have more efficiency losses than fixed multi-piston calipers. A lot of times you can see that right on the pads, as they tend to not wear evenly on the single piston sliders.
Don’t get me wrong, I’m not saying I’d switch to the wilwoods. With the 11.75” rotors, for my money I’d keep the factory single piston sliding calipers. They’ve worked great for me for 70k miles on my Challenger. But I also don’t think the Wilwoods will be a significant decrease in actual real world braking force. I’ve done the math, and the efficiency difference between the single piston sliders and multi-piston fixed calipers can probably account for most of the difference in the math.
If there isn't more going on than that, even a Viper caliper would lose to a factory 2.75" single piston caliper in clamp force. And that's not real world.