I used an RB #6 for breaking and it never went bad. I did shim to Andrea's recommendation though.

Just an FYI, here are the replies I was sent (regarding breakin with 30%):

Hello Mr. Torres,

I would check to see what Sirio recomends in the box (I'm not sure what
their instructions say). If I remember correctly, their engines are usually
set for 16% nitro but I know they shim them for more nitro so people don't
pop them straight away - If I had to guess, I think it would be fine with
20% and even 25% but going to 30% you may want to add a thin shim just to be
safe - definatly wouldn't be a bad idea to start especially when you are
breaking the engine in. Later, you can take the shim back out and keep and
eye on the glow plug (if it breaks or appears "frosted" then you know the
shimming for your nitro % is too low...

Josh

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The std set up of our EVO3 engine is made to use a percentage of 16-20% nitro fuel.
I suggest you in order to avoid problems to add o,1 mm shim at your engine for the brake in procedure.
After the first operation you can check about your need accordingly with your air pressure.
It's difficult to tell you the exactly set up of the engine as it depend from many factor.
Adding one shim you'll avoid demage during brake in.
Regards,

Andrea Rossi