Slotted Rotors

[jeep/bronco]

as far as upgrading the brakes on a mini kudos to you i would have done the same thing those little cars are light yes, but they are absolutely ridiculous on the track a bone stock cooper s would run times similiar to my 360hp e36 with pss9 suspension, they are really nice little cars (they are made by bmw ya know..lol) on an xj i can see upgrading to a larger rotor and maybe a dual piston caliper and a quality pad but to use a slotted or drilled offroad just seems that your asking for problems. and unless your going to track your xj or use it as your tow rig i cant even see doing that much unless your going up to 35's or bigger and still driving it on the street. at that point you have increased the rotating mass drastically and a brake upgrade is needed. my jeep on 32's will not have a brake upgrade other than pads and maybe a brake booster upgrade (my bronco was swapped over to a f250 system that was night and day difference on descents)

 

[Ronbo]

Going with the 'cheapest rotors you can find' isn't what I'd recommend.
My XJ came with the cheapest rotors Jeep could find, as well as a few hundred thousand other Jeep's, and they were all recalled for poor performance. Mine warped any time I actually required the vehicle to stop quickly.
I upgraded to Powerstop rotors 140k miles ago and still have the same set. EBC 'Yellowstuff' pads have higher friction compound than any of the other pads I've used, and I'd bet I could warp most cheap rotors, in much the same way I could the factory junk.
I don't race on a track, but I do tow my camper through the mountains, and try to bring 35" MTR's under control either on the street or dropping of ledges on the trail. I've had no regrets, ever. $.02