David, you ought to be able to find a high mileage NA Supra for a lot less than that.
Predictably, I'd vote for the Supra. Why?
1. Easy to upgrade to TT brake calipers, rotors, and aftermarket rims.
2. Deeper wheel wells (I think), so easier to stuff bigger rubber in there.
3. Slightly lighter - an NA hardtop with 5spd should run around 3250-3300 lbs, IIRC
4. You can't go wrong with the Supra's 6spd drivetrain; it'll take anything a ?UZ motor can dish out, including high boost and/or NOS. Granted, if you buy a 5spd NA car, you won't be getting all the good bits that come standard with the 6spd package, but you can always pull them off a wrecked 6spd, and there's no lack of those. And you'll have the comfort of knowing they'll bolt right up.
5. Although it's not a Lexus, it certainly fills the bill better for a maxed out, "extreme" performance project.
Hmm, would it then be called your "Sextreme" project, instead of "Lextreme"? That might be a hard sell to wifey :veryhappy
John