Angier,
Lots of good questions here:  In did reduce my inlet size and did pick up 5 kts, but what lies down stream of the inlets will have a more significant impact on drag than the small change in the inlet diameter.  Any leak in the system will allow more air to flow through the inlets.  This causes the inlet velocity ratio to go up.  Shrinking the inlet diameter also causes the inlet velocity ratio to rise.  As this occurs, more pressure recovery is done behind the inlet rather than in front of it.  Pressure recovery downstream of the inlet is more difficult and will require good diffusers.  A 100% sealed cooling system requires surprisingly small inlets.  NASA report CR 3405 is a real eye opener on some of these topics.  Here is a link (large file, 8MB)
http://www.n91cz.com/cooling/Copy_of_NASA_Cooling_Report.pdf

Chris Zavatson
N91CZ
360 std
www.N91CZ.com