I was looking to buy an ma7o supra before i got my z. The 7mgte is pretty tough with a metal headgasket and properly torqued arp studs, however even then, i wouldn't expect it to last all that long. 20 psi seem attainable on a stock bottom end, but that would require a new turbo, as the stock one overspins at about 15-16 psi or so ifrc. Once the headgasket blows though, its very likely to develope rod knock. Be weary, cause if someone drove there supra with a bhg (yeah, a commonly used acronym for blown head gasket on the supea forums), there a good chance the motor needs to be rebuilt.
Styling is subjective, but i prefer the sleek look of the ma70 to a z31.
Personally i would take mkIII supra over a z31, but thats just me.