@Switchblade, the Alpha's kit does look great, but I just couldn't justify spending $2,000 more than the StopTech Kit. BTW, almost any pad/rotor combination can lock up the wheels. It's what happens after repeated steps (hence the fade and warped rotors). Enlarged, Slotted, Drilled, Vented, etc. are all done to remove heat and get the temperature of the rotors down. What a lot of people are really looking for is pad "bite", or how aggressively the brakes slow the vehicle down with minimal effort. There's also a "force" curve as well, just like how an engine horsepower comes on. Some grab great at first, then taper off. Most race pads are very linear and consistent. Back to temperature. On the street, this can work against you since if there isn't enough temperature in the pads/rotors, it won't stop as well as when they're in optimal temperature range. So far, the kit I have seems to do great in both scenarios. I don't have experience with this setup on the track, though, but @Noel Hughes has run them at the FIRM track and said they're great, so they're probably good there as well. Make sense?
BTW, where are you located?
Just a couple quick notes -
Here is a good example of the force vs. temperature for Hawk Pads -
It is very important though that when picking brake pads that you work in the heat range that you are driving the vehicle. On the Slingshot, there is not a lot of mass to stop since the vehicle is relatively light and the rotors are actually rather large for the weight of the vehicle and its weight distribution. If you go with a pad that is overly aggressive you may never get the brakepad into its ideal operating range, which a lot of the times means lower coefficient of friction, more dust and non-linear braking force.
As for the big brake kits, the 4 piston or 6 piston setups if sized correctly will not apply more force to the pads, they do provide that force more evenly across the pad surface though to prevent tapering of the pad. All of the big brake kits I have seen use larger pads, our DDMWorks kit, Alpha's or Stoptech's all have larger pads than stock. The larger pad volume has the benefit of higher thermal mass. This higher thermal mass of the pad helps with temperature spikes under hard braking, takes more energy to raise the temperature of the pad and also the larger pad volume helps with longevity. The big brake kits also have larger rotors (14" on our DDMWorks kit, 13" on Alpha's, etc.) which also have more thermal mass also. Larger thermal mass of the rotors allows them to absorb the initial thermal load under heavy braking and since all of the aftermarket kits have better vanes internally, typically directional, they are able to disapate the heat faster than the stock rotors also. One note with the big brakes we found during testing of our kit, with the bigger pads and rotors it is actually difficult to get some of the more aggressive pads up to operating temperature at all, unless you are doing hard braking repetitively with sticky tires.
The other big factor to consider with braking is your tires. No matter how good your brakes are, the tires are what contact the ground and actually stop you. So if you have some really sticky tires, you can go with more aggresive pads because you can develop the higher friction with the road to stop faster. If you are on stock tires you really do not want to go with something too aggressive, otherwise you will just engage the ABS and never really get the pads to their operating range.
The slingshot setup stock is not that bad, mainly just a pad replacement takes care of most people. The 2 piece rotors are nice and offer better cooling and less rotational weight and with a pad upgrade definitely takes care of almost everyone. The big brake kits are typically not needed unless you are doing some hard track days with sticky tires, although they do look great 
Hope that helps,
Dave
