Rear disk brakes will make very little difference to your stopping distance. Good blank front rotors, good pads and stainless lines will help much more. Sloting and drilling is just cosmetic, and if anything removes surface area that could be used to stop your car, they won't help your brakes run cooler. That said, rear disks do look a lot better.

Another thing to watch out for, my friends '96 CX has a 13/16 MC. My '98 EX has a 7/8's. He put rear disks on his and the pedal has more travel now (you need a lot more fluid for a rear caliper than you do a drums small cylinder). He's planning to swap some EX front disks and an EX's 7/8" MC eventually (trust me, there is no air). The EK ('96-'00) MC's also have different hardline connection points than the EG Civic's and DC Integra's. You can rebend the lines to match up, but it might be tight (one of the EK lines comes straight down into the top of the MC). I'm not sure how big the Si MC is, never looked at it.

I don't like kits like the AEM big rotor setup. Bigger rotors will absorb more heat so they'll last longer before fading, but Honda's weak point is the single piston cast caliper. When your bleeding them, you can physically see the caliper flex when you pump the brakes. That can't help give you a solid pedal. You'll see better improvement with a kit that replaces the caliper with a multipiston stronger unit.