a true comparison between the two needs to be done between two STOCK cars. Your Z has been modded and the Supra has mods to, but not up to the same level to the your Z.
Anyway... I too was looking at a Supra last year and got to test drive it. I really liked the tranny and the power, but the handling seemed like it was not so tight(it was stock and it may have had worn bushings), but was pretty nice. I decided not to buy the Supra since I figured it would be in my best interest to mod the Z, than to have two cars to try and figure out a parking spot for.