I have a similar dilemma. I've got the 6 pot KAD front calipers with grooved 356mm 10 groove front disks but on the rear I have the (more than adequate) UK spec calipers and plain Toyota disks.
Now, I could change the rear disks to grooved ones so that it better matches the appearance of the fronts - and I'm tempted to do that - but on the other hand I'd feel like a tart because taking off the excellent Toyota OEM disks and putting on some flashy aftermarket tat is probably a downgrade in reality.
By the way, I don't think Brembo make disks for the stock Supra, do they? Ain't they just the 3G ones that folks claim as Brembo?
If you like the flashy look, I know the DBA Gold disks are popular.