I've run Hawk, Porterfield, and Carbotech on the street and track.

- Weight of the car is my big one - For a heavier car, something like an HP+ is exactly as Nick describes. Works great, then falls off a cliff. For a light car\low power car (sub 2300 lbs), it's a different story. One of the LeMons teams I've run with has used the HP+ successfully with ducting for hours at a time on a Honda. The car won't break 115 on a long straight at VIR, so you can pound on them for hours if you are smart. I did manage to fade them, but that was me being too aggressive in an enduro situation.

- I've also run the HT-10 in LeMons racing, and that just seemed like too much pad for street tires. This was on an E30 shod w/ Azenis. We had lots of lockup problems at CMP. The HT-10 seems better suited to r-comps and ABS.

- I've run Carbotech XP8 and XP10, and they work really well, but they wear VERY quickly.

- I've run the Porterfield R4S and R4E on track. The R4S is similar to the Hawk HP+, but without the initial bite of the Hawks. Wrong pad for heavier cars. OK for light/low power, but not that great. The R4E is an old endurance compound that still works well, but it does nothing exceptionally. They are expensive, but wear very well.