OK, understand that I LOVE Mustangs: Brute simple, but effective and quick.
But, for the money, I would go for the Lexus. It will depreciate less, use less gas, and most likely give you fewer problems. Plus, it has a certain cachet which can be good as well

Yes it's less power. I guess it all depends on what you want the car for. If you are going racing, then I think that your decision will be REALLY simple. If you want a daily driver, I would say go with the Lexus.