Chris, 

I have G900X / Sorceror / IO550N in my Legacy and updated to version 10 in October; Gary Lane at Lancair accomplished the upgrade and checkout in one day.  I've seen some of the same issues you have:

1.  Fuel flow reading lags.

2.  Sorceror altitude reads 1foot higher.

3.  Altitude select on G900 takes several seconds to reach Sorceror.

4.  Many setup items requiring lots of experimentation to get right.

5.  Max fuel quantity doesn't match the airplane's actual max.

6.  Fuel pressure annunciator bongs during taxi.

I have not observed the pathway error that you mentioned.

Never having been used to version 8, I took these to be "features" of the system and have been living with them.  

The other issue I've had is thet Sorceror going "Glideslope Armed" way out before even reaching the initial approach fix, then GS Arm goes away during constant altitude segments and has to be re-armed by canceling and re-enabling GPSSteering on the intermediate segment before G/S intercept.  This problem, and the lag in the altitude select getting to the Sorceror, are the only two glitches that really bother me.  The rest are just annoyances.

Charley Brown

N550KC