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Some of the ford probes had very aerodynamic mirrors as well, I would suggest taking a walk threw a pick and pull/ salvage yard and look for the least aerodynamically obtrusive mirror you can find.

For me the New Beetle European drivers mirror mixed with the North American passenger side mirror would provide less drag.
Doing it this way you would be using the small mirror from each continents mirror set.
This may be the case with other cars in Europe and North America as well.