That is actually a nice kit and will offer improvement as you have larger rotors. Big brake kits are better mostly because the rotors are larger not because of the caliper design.
I would have to disagree the caliper plays a major part in big brake kits I would rather have a six piston caliper vs a two piston caliper any day. There will be a noticeable difference using 14 or 15 inch rotors on a two piston caliper but will have nothing on a 16 inch rotor with six piston calipers stopping distance will be far apart
Not trying to start an arguement...but have you tried it? I have done this on an Audi S4 I had a couple years ago. Stock caliper, new carriers and rotors that were 2" larger in diameter (don't quote me on that...if I remember correctly it was 13" to 15")...HUGE difference in all respects. I couldn't believe how much of a difference it made. I get what you are saying and I am not trying to discount that bigger calipers are going to be very effective as well. It's all part of it but the leverage on a larger rotor is a big, big part of it. There is only so much pressure that can be applied to the pads no matter how many pistons it has but it won't necessarily change the leverage. It's easier to stop a big rotor than a small one.
The stock caliper is not exactly crap either...it was designed to stop a really, really heavy vehicle and performs reasonably well with good pads/rotors in stock size. The arguement here really is if the larger rotor kit would be an improvement over stock and I think we can agree it would be even with stock calipers. A big brake kit with 6 pot calipers is the cat's meow but often is cost prohibitive. If money is no object, I agree it's the way to go. Just trying to point out that larger rotors will offer a huge improvement and the kit can't be beat considering any quality BBK is gonna cost you $2k or more.