I'll rebutt. Actually yes, the six has a few things the four does not.
First it has additional pistons, the area is a bit more 3.9 vs 4.1 sq in. That means a bit more clamp load for given pressure. Small, but there.
The real benefit is it is a closed bridge design caliper. This means it is much stiffer and will likely result in a slightly shorter pedal and more linear pedal pressure.
All of this is more important the harder you use the system. If in reality the car is a cruiser which sees the track one time a year the six is more for looks and bragging rights, but as the track time goes up, so too does the benefit. But so to does the cost, the weight and the size.
This caliper is nearl 1/4" wider ON ONE SIDE than the standared BSL unit. It also weighs abou twice the amount. Cost is and extra $225 over base cost.
Keep in mind howeever that the initial plan for the car was an affordable alternative to others on the market. This meant that the choice of base parts was limited. The features of the systems is that you can 'upgrade' as things and buggets change.
mike, how much money do you have? this is where the question you asked has the answer! i have run lots of laps on lots of tracks, but never more than 40 minutes at a time (3 mile track) i am still using a factory single piston set-up. i did melt the factory pads and calipers at 24,000 miles, 325 miles of that was high speed track time, and loads of autocross events. true, its not the best, but i am able to transfer my money into mods that make my laps times decent! ok, so the math is there why to buy multi piston, but once you can master your car, the old saying from racers will apply....slow in, fast out! this means a huge brake kit is not the big lap time lowering solution! this is just posted to help some of us po'boys still go fast and i dont have all the answers, but my finish's at the st.louis events might say something! when (which will be never) i ever decide to race door to door in a long timed event, i will go multi-piston set-up, but i bought a beater camaro to do that with. in summary, yes there is a big benefit to multi piston, but i cant say its worth it for me.