Go to the source
I find Van's performance numbers give an excellent benchmark:
160HP, RV-9A, at 75% pwr @ 8,000 = 162Kts
I have found Van's numbers are not smoke and mirrors but real numbers the average/typical/nominal RV can reach.
I don't know what all the fairings are worth? My guess is 10-12mph (8.7-10.4). So if you pick up 10 kts you will be beating Van's numbers by 3kts. That is possible, reasonable and very good, but it is also with the variation of measuring TAS by common methods.
When reporting TAS it is hard to tell how accurate that value is. If you are just using your airspeed indicator you need to know how accurate the indicated speed is (i.e., CAS-calabrated airspeed or corrected IAS). Airspeed indicators can be off by several knots. Even if the gage is calabrated on a bench, the static system on our little planes tend to have "noise". That is why during flight test of even the biggest planes they drag out a static source on a line behind the aircraft. A suspended static/total press head called the BOMB is feed out on a line pulled behind the plane by 100's of feet to get a good static/total presure readings away from any disturbance.
http://www.spaceagecontrol.com/news100800.htm
for just static they have cones
http://www.spaceagecontrol.com/trailing-cone.htm
NASA notes on how to measure airspeed
http://www.spaceagecontrol.com/naca-tn-616.pdf
If you are using ground speed from a GPS and doing a triangle or 4-leg average to factor the wind out, that might be a little more accurate, but still you can have tolerance with just the GPS speed value alone of 1-2 kts.
The air mass (wind) is not constant (horz dir)through out the legs, so you can have variation of a few kts. Up and down drafts also cause TAS airspeed variation. Air is never perfectly still in any direction.
How accurate is your altimeter? How accurate is your OAT gage? How accurate are your engines gages, MAP & RPM (% pwr)? All these add error.
From what you say you are in the ballpark on the fast side. Also make sure when reporting or comparing you are at really at 8,000' equivalent pressure altitude corrected for pressure and temp (density altitude). Also check you % power against the power chart. If you are fixed pitch and over revving you might be a little more than 75% pwr.
With a standard base line of 8,000' @ 75% power we can compare our performance, but the accuracy will never be within less than a 1-3 kts range, even being careful. So bottom line 155kt dirty is realistic. For the other Gent that is 155kts with fairings, you may be going faster than you think?
Congrats on your Fast RV-9A George
