I've been using the Carbotech 1521 (Bobcat) pads for street/autocross for a few months now and they've been working quite well. There is a little bit of squeak now & then with slow stops. They have good bite for autocross; I am sure the AX pads will be even better, but so far these have been doing fine.
I do have the Brembos, but I doubt there will be much difference for the standard brake setup for this use.
I like the AX6 autocross-specific pad from Carbotech a lot. We've sold a lot to autocrossers who liked them. But dual-purpose? Mmmm... while they DO work dead cold, they do make some noise.
http://www.ctbrakes.com/brake-compounds2.asp
Carbotech™ AX6™
The AX6™ is specifically engineered for Autocross applications. A high torque brake compound delivering reliable and consistent performance over a very wide operating temperature range of 50°F to 1000°F + (10°C to 537°C+). The advanced compound matrix provides an excellent initial bite, high coefficient of friction at lower temperatures along with very progressive brake modulation and release characteristics. Many drivers use the AX6™ for street driving as well, even though Carbotech™ doesn't recommend street driving with AX6™ due to possible elevated levels of dust and noise. AX6™ is NOT recommended as a race compound in most applications.
I used to swap pads (and rotors!) between a street/autocross friendly set-up and a track-worthy set with harder compounds. When we moved to Carbotech we realized we could use their different compounds on the same set of rotors without "cross-contaminating" the pad materials. That saved a LOT of work, and we have folks who switch between AX6 and XP-series
Carbotechs for street/autocross and track use.
As our car has increased in speed on track, and our brake size hasn't (we stuck with the 14" Brembo front/14" GT500 rears for a long time), the weight and speeds have really taxed the brake system. We've moved up steadily to the hardest compound XP20 pads they sell. And moved up from 3" to 4" brake ducting, to keep pad temps down.
But as I street drive this car less, I also seem to care less about the noise of the harder track pads. This year we've still autocrossed this car a number of times on the XP20 pads, on both Hoosier 315 A6s, Hoosier 335/345 A6s, and 315/335 Rival street tires. Won at Goodguys, won at Optima/USCA (with autocross, track and speed stop challenges), and always with the same XP20 pads.
We just ran an autocross yesterday in our TT3 prepped Mustang on Carbotech's hardest XP20 pads, in the rain, too. How do we get the pads up to temperature? Drag the brakes from paddock to the starting line in 1st gear. It takes about 5-6 seconds to get the pads to SQUEAL, which is when they seem to be hot enough to work. Ever since I started doing that I haven't come to a first corner and had no brakes in an autocross.
My results at yesterday's SCCA event were pretty poor, but it was still the 8th quickest time out of 145 entries, and it wasn't the brakes holding me back (it was a course that went from wet to "drying"). So nowadays I run the same pads for track and autocross, and if I were to daily drive the car a lot I'd switch to the Carbotech 1521 pad. Easy.
Carbotech isn't the cheapest brake pad choice - the lower cost options tend to have more filler material and wear more rapidly, from my experience - but it seems to have the best price

erformance ratio. We've tried ALL of the top named brands, and sell many of them, but stick with Carbotech for our own cars and what we recommend (and we make less money on this brand vs others).
edit: for STREET use I wouldn't use any of the XP series pads or even the AX6. The 1521 is the one to go with... its the dual-purpose street/autocross pad that works dead cold and makes no noise.
Cheers,