you need to reclassify your cars. A lexus is300 no matter how much power it has isnt a muscle car. They are both sports/luxury cars and will stay that, just with more power.
Id go with the a4, plenty of power as is, room for more, and youll know whats going into the car. unlike buying someone elses work/problems/abuse, especially if the lexus cant take a simple turn.
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