Perhaps you should look into burning less fuel-vs-carrying more.  A 4
cylinder 200 HP IO-360 might get you closer to the design goal.  Running
lean of peak with an electronic ignition should bring your fuel burn down
considerable to 1/2 of what a 6 cylinder is burning without a 50% cut in
speed.  The aircraft would also be much lighter.  The factory Legacy
originally flew with an IO-360.  (turbo-normalized I believe)

Micah Froese
Lancair Legacy 2000