I have those springs on my car now. I think they ride pretty well. I have the Tanabe springs with the KYB AGX shocks and it is a much smoother ride than the Eibach/AGX combo I had on my Eclipse. Not sure if the Eibach Prokits for the Supra are the same spring rate as the ones I had on the Eclipse, tho. The only thing I don't like about the Tababe Precedos are that they are too low for my taste. I can still get over speed bumps, but I have to go really slow and I actually scrape on the really big bumps.
So, I am actually switching to the Eibach Prokits to give me some more clearance. Let me know if you want the Tanabe springs, I can give you a good deal on mine once I swap them out. Hope this helps.