As mentioned by @
DAEMANO, I don't agree that RR Racing choosing not to respond with simple specifications indicates that they have something to hide. I can't find any publicly released piston sizing information for the APs kits with a quick forum or Google search either although I'm sure you'd be happy to release that info to anyone who asks for it. For the sake of disseminating information, I will comment on the RR Racing sport performance (4 pot) front BBK because I bought one.
When I first got the kit (a few weeks ago now) I measured the pistons and recall they were ~38mm based on my eye and a crappy school book ruler. The rest of the relevant info is available on their website so I stuck the values in a torque calculator and came out with a slightly higher torque value with the RR Racing front kit than stock. I did this a while ago so I don't remember the exact values but my point was that Rafi mentioned this was the case so I can confirm he never said anything misleading or incorrect.
I realize it seems the real issue CSG and JRitt have is the claim that increasing rear bias is beneficial when their own findings indicated that wasn't the case and are looking for data from RR Racing to back their claim up. I'm not going to lie here, I DO think the rear kits are primarily superficial especially for cars with no rear downforce so I have no plans on getting one.
In the end, I'm of the opinion that AP's caliper and rotors are the best so if you want the best, you need to pay the extra to go with AP. In my case, I'd love to get an AP kit but the reality is that I cannot pay for it now or in the forseeable future. If an affordable alternative never appeared, I'd never be able to upgrade. Suggesting that I save up for it isn't helpful because I'm also saving for a house and every dollar spent on something else is a dollar that doesn't go into the house. This is why I look for products that are 70% of the high end product for 50% of the cost and RR Racing has released an offering that appears to be in this range, targeting people like me.