Additionally, (re:1 vs 2 disks) while a person may be able to "lock the front wheel with one disk" and a mighty mighty pull, the notion of being able or not being able to "lock up" the front wheel with a single disk is not even anywhere near the point.
Two disk setups provide a better response ... or "feedback curve" .. for the rider when riding near front wheel traction limits, aka "threshold braking". Sure, a single disk can lock up the front tire easily enough, but the difference between "wanting just a tiny bit more braking power" and eating major shit resides on this tiny itsy bitsy little sliver of a response curve.
Twin disk setups make that "touch and go" zone on the brake lever much longer, the graduations of braking force are sortof "reverse exponential" (not sure that's even a thing, I just kinda made that up). If anyone reading this is experienced with electronic components, the twin disk setup is sortof like a reverse log potentiometer ("reverse logarithmic" vs "log", or "logarithmic") where the most touchy portion of the pot's curve is at the end of the sweep, instead of at the beginning of the sweep or instead of being "linear" or having a straight line response). The closer the brake gets to it's locking point, the LESS sensitive it becomes. The response curve of the brakes actually becomes flatter, not steeper, towards hydraulic locking pressure (the point where the pads grab the rotors better than the tire grabs the road) and face meets asphalt.
With a single disk setup the brake lever is less forgiving, the point between braking and locking is touchier, more sensitive than dual disk systems. That hyper critical area of the response curve is much steeper, things happen much sooner with less time to react.
As well as the advantage of shedding heat far more efficiently, which is great for riding two-up with your not tiny significant other when coming down that mountain pass that you took all morning to climb and enjoy the ride. Speaking of under engineered brakes, I got into a spirited ride down the front side of Sunshine Pass (near Jacumba close to San Diego). A six thousand foot drop covered in about 45 minutes on two Harley FXRs (my dad and I, my wife on the back of my FXR). Well, long story made very short, the undersized (but cool looking! oh brother) dual disk front brakes of that HD were about worthless by the bottom of the run. My dad commented on a pass I made on him at about 105 mph while entering a left turn marked at 50mph. I didn't want to tell anyone that I had little choice in the matter since when I grabbed the front binders to check up going on that particular turn I had basically nothing but a handful of overheated brakes. The bike weighed 650 wet, add the passenger with her gear/helmet/leathers and that put the entire machine at about 850 pounds total less me. Wrestling with an 850 pound HD with hot brakes and a severely overheated sense of competition with my dad down that mountain was a ride I'll never forget (I haven't even bored the hell out of you with the part about how we caught a group of sporties on new Interceptors, those guys totally freaked out when we saw them later ... "you guys are on HARLEYS?!?!?" Heheh....) Anyhow, I just acted all macho, like I did it all on purpose (I'm sure no one here has ever done that before ... yea right!). Days of youth.....
So anyhow, that more forgiving braking curve is another thing going for the dual disk setup. Then again the single rotor system is, after all, at least five pounds lighter. Hmmm ... much to think about for someone stuck in this position.
Presently my choices are being dictated by money, or more accurately the lack of money. Used sportbike stuff is pretty cost effective sometimes. So for now until more of the dead presidents show up I'm kinda going with whatever stock stuff I can afford.
But man oh man can I bench race with the best of them!!!!