Steve, I don't think they are really an option, not much heat is generated at idle/taxi speeds, just weight and drag you don't need. other aspects will be at play like your exits etc.
There was tufting put inside a Bonanza cowl a few years back which showed complete reversal of flow through the cowl, explained why it would cool better on the ground with wind up its ass. prop probably sucking the air out.
I think this airflow stuff is sometimes dark magic.