I like the comfort of a 4 door, your car sounds like a rocket, I do feel that 15% increase in your car's fuel economy is to high of a penalty for the 50 more hp you may or may not use. Offhand my suggestion would be to throw a medium size turbo on it and use the boost when you feel like it a.k.a put your foot down..
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Save gas
Ride a Mtn bike for errands exercise entertainment and outright fun
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