You see there are engineering standards when it comes to measurement and test methodology , in case of speed flutter measurement AES clearly states 3150Hz test tone must be used and measurement taken using 2-sigma meter , there is much more to it like using notch filter to compensate for speed wobble due to record centering and to discard turntable bearing effect . Not sure how you tested speed with oscilloscope unless you meant frequency meter .But the thread is about fitting a new cartridge to a Rega RP6.
“Speed check I cannot see any other way than reference tone played on the turntable as you need to do it real life with cartridge drag taken into account , some manufacturers like SME set speed bit higher to account for it .”
Stylus drag is a very contentious issue. I would put forward that any turntable drive system that slows under stylus drag is improperly designed. I have looked into the whole subject in depth and made many measurements (including using test records). It is certainly not a given that platter speed varies under load.
However, if you use a 12” strobe disc and a 10” EP record it is possible to use a strobe whilst a record is playing - I have done this but I have also used test tones and Audacity and a scope etc.
———-
I actually have a bunch of test records that I have acquired over the years. However, I still adhere to the belief that, for the vast majority of enthusiasts, they are of no real value.
As I said no point arguing about I will use test records you don't so be it ,
PS : if you like I would gladly buy yours depending on what you have and condition.