I am running the Kevlar lines and they are amazing! Best mod I have ever done and the brakes feel like reverse thrust on a 747.
Ok they don't feel any different from braided steel.
It's cool to say I have it though. Some say Kevlar can burst but I understand that issue is fixed. Lots of pro racers use them so I figured I needed them as I'm as fast as they are right?
To me the brake mods go in this priority order:
1. Steel lines - Improves feel and power. Basically a muct do mod on the Busa.
2. Double H pads - Improves bite. Big difference in bite actually. Helps overall power too. This is cheap and easy so it is easily the best value for the money.
3. Radial MC - Mostly improves feel and control in modulating the brakes but not absolute power typically. This is expensive but it brings the Busa brakes on par with other sportbikes.
4. Caliper upgrade - Improves everything basically. You only need this if you ride fast but it is a clear improvement. This is expensive but worth it to fast twisty riders
5. Rotors. - Short of a warp or extreme gouging of the rotor this is a cosmetic change IMHO. Wave rotors do cool better I hear, but I have never had the OEM rotor overheat.
Items 1 & 2 are mostly about getting the power of the brakes up to the task (Suzuki should be shot for the OEM brakes). The rest are about getting better feel and control on the brakes. I have the Brembo MC & Calipers and these are a pretty surprising weight reduction too. Lighter rotors would help turning I suppose, but not sure that it would be noticeable in street use.