Hi,
Not sure what you mean by "real speed" - I meant indicated as on the Airspeed Indicator. As noted I reckon on a True airspeed of about 90 knots, but that will vary with altitude etc. My GPS shows my groundspeed, but I haven't done the fly 3 perpendicular legs, noting groundspeed, then do the maths to work out my TAS from the GPS as per http://www.eaa62.org/technotes/speed.pdf
Cheers,
Neil