Ron,
  Keep in mind, I have a Lycoming IO-540, which I hear is a little
thirstier than an IO-550.
  In the climb, I go at wide oprn throttle, 2700 RPM and rich enough to
maintain around 350 degree CHT, a technique recommended for normally
aspirated engines in the Advanced Pilot Seminar.  That results in 22-26 gph,
depending on altitude.
  My cruise flow depends on altitude.  I fly wide open throttle and peak
EGT in cruise.  (Lycs don't seem to run as smoothly LOP as Continentals).
That usually gets me around 190 KTAS in the low to mid teens where I usually
fly.  FF runs between around 15-16 gph down around 10-12,000' to as low as
13 gph around 16-17,000'.  If I'm lower than that, the flow runs higher.
17-18 gph is an average when I'm down low.
  Flat out, full throttle and full rich at sea level I burn around 26 gph
while indicating around 200 KIAS.  I think I've done that about twice to
satisfy my curiosity and now try to fly up where the air is cool and the
fuel burn is about half as much.
  Skip Slater
  N540ES