Model A rear tire size verses cruise RPM

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I have a stock 31 A Tudor with 5.00x19 tires on it now. I would like to lower the overall RPM at cruising speed by changing the rear tires to either a 6.00 or 6.50.
In stock form is there enough power to use tires that size? Eventually I’m adding a different head and intake.
I’m running excelsior comp H’s, Coker lists the diameter as 30” but they actually measure 29”. Does anyone know the exact size a 6.00 or 6.50 is on a stock wheel?