Fade, from what I've researched, comes more from the pads than from the rotors. If I recall, semi-metallic would be the choice pads to use for street/DD on a GT car like a MkIII. I don't know what OEM is, but if they're organic pads, the only improvement you'll see with slotted rotors over stock blanks will be provided by the slots only... at the expense of longevity.
As for powerslot, I would stay far, far away from them:
http://www.mvpmotorsports.com/Templates/frmTemplateM7.asp?SubFolderID=330&SearchYN=N
MVP is a dealer, and they say:
Made in Taiwan. Low quality in our opinion, not recommended. But if you want them we can supply them.
We highly recommend you spend a few extra dollars and get the made-in-Japan Rotora rotors instead.
Upselling or not, for the whole ~15 dollars per rotor difference, take it for what it's worth.
As for pads, Porterfield R4S Street Brake Pads are what I would recommend for street use. Low dust, quiet, and good longevity, from what I've read about them. If someone has firsthand experience to the contrary of that, I'd
really like to know (before I spend money on it).
The only downside I've heard anyone say about Brembo's is that they are
much thicker than stock rotors, and will rub for a while until the pads wear down to provide a gap... but a thicker rotor will be more advantagous later anyway, so in reality it's an upside. Brembo only ever made blanks for the mkIII Supra, anything slotted or drilled with Brembo next to it will be a blank that's been aftermarket machined (which is not so good for longevity).
Upgrading your pads will likely net better fade characteristics than upgrading the rotors will. Slotted/drilled doesn't have all that much effect on really good pads.
Hope this info helps, good luck.