Long story short I had my 582's sleeves rebored and fitted brand spanking new 1'st oversize pistons
We did the run-in and she's running beautifully and not leaking a single drop of oil or water anywhere (and the rotary valve oil reservoir is now maintaining its level 100%

So generally I'm very happy but the problem is its not getting the expected revs
We have another aerie (A) with standard size pistons which gets max 6200rpm with its own NC prop on the ground
My aerie (B) currently only gets about max 5900rpm with its own NC prop on the ground
Now if we put aerie A's prop on my aerie B, my aerie only gets max 5800rpm on the ground

Shouldn't my brand new oversized pistons and sleeves be getting at least the same or better revs/performance as aerie A's engine?
We also put in new spark plugs and measured the clearance between sleeves and pistons (0.05mm)
What could be causing this?
Could it be the that the exhaust is faulty/dirty or must the engine still get 'loose' (400rpm difference is a lot though)?
Or what else can we try please?
Many thanks in advance
Ant