A question about rpm

Which is likely to be more accurate - the rev counter or MEMS 1.9? I discovered during the Silverstone track day that the rev limiter cuts in just before 7100rpm on the clock, so have I actually got more rpm to play with than I thought, or have I just been going slower than I thought? I don't believe the speedometer as it's 10% fast where I've been able to check it, and it could be better or worse at 100mph. With the breathing mods I've got I can now use all the revs, so I'm just curious as to what max speed I'm getting down the Hangar Straight!

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