For example, my aircraft stalls in the approach config. at 64 knots after a MTOW. So near enough to max weight of 816 Kgs (1800 lbs).

That is a minimum approach of 83 KNOTS.

Pucker factor means I approach at 90 KNOTS, and bleed to 85 over the fence.

Dom,

 

Comparisons between homebuilts are interesting at best.  I have talked to many 320/360 builders where the initial weigh-in differs as to where fuselage stations are (FS), weight distribution on each of the wheels and the final calculated arms for pilot, fuel, etc.  Sometimes, the empty weight CG is suspect.  This would seem to be relevant at stall.

 

It would be nice for all of us to use Kts - after all, it is the modern generally accepted standard for aviation.  But, no one reports Calibrated Air Speed, a more useful number.  Some of us have done our best to find this number at various speeds and if we have the Rocky Mountain Instrument's (RMI) Micro-encoder, it can be adjusted so that KIAS is very close to KCAS.  Using KTAS and a GPS derived KTAS, a correction factor can be determined- RMI computes KTAS, accounting for compressibility's affect (miniscule at low air speeds) on the true air temperature and using pressure altitude - other computers may not.  Modern GPS units are quite accurate and there are several techniques available for determining the derived KTAS. 

 

Usually, the largest inaccuracy of a pitot/static air speed system is at a high angle of attack - like close to stall.

 

However, I generally fly much like you do on approach, as confirmed by an AOA indication.