Your current setup actually looks pretty good, I don't think you will get much better with a car like that unless you want to take the trunk lid off (or build a custom one) for when you are using your car as a bike hauler.
I am so used to SUVs and trucks where 5mpg is a big deal, how much extra fuel are you burning with your 5mpg loss? is it actually significant for an occasional trip with friends?
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