Teq, I'd go with the best rated tire all around if its a stock original Supra why not white letters??
That would be a personal preference thing, but aren't they only white letters on one side? Can't you have them mounted blackwall out?
Some years ago, I was watching one of those muscle car auctions on TV and it struck me that at least nine out of ten cars across the block had BF Goodrich T/As. I think its partly because there's not much else available in 14 and 15 inch diameters, but also because if you're going to have white letters, its the better looking tire. And as to speed ratings, when are you ever going to go 112mph + for long enough to overheat a tire or even at all.
I've bought a bunch of T/A radials over the years. The only bad thing is some batches have suffered from "blooming" where they get a brown discoloration over time (a very short time). Its something to do with a chemical additive that's supposed to protect the tires from UV damage. Sometimes they get a little too much in the mix I think. Its a pain to clean them. Bleche Wite used to work, but when it was bought out by Black Magic, they changed the formula and its totally useless now, a waste of money. The only thing I've found that works is Goof Off, which is rather expensive for cleaning tires and probably isn't all that good for the rubber. I suggest if you like the Coopers, researching whether they suffer from "blooming" and if they don't, I'd maybe live with the slightly wider tires over cleaning the T/As. But I've got some Toyo's on another car that bloom really bad and some Goodyears that do it a little bit too so its not a unique fault of the Goodrich factory. And its only some batches. I have some T/A's that are fine.
BTW, if anyone has found a cleaner to replace the old Bleche Wite formula, I'd be most appreciative if you'd pass it along.