By my calculations: (based on the stock 74mm S/C Pulley)

Stock Crank Pulley : 74mm S/C - - Ratio = 2.0270
Engine RPM @ 6,000 - - S/C RPM = 12,405
Engine RPM @ 6,200 - - S/C RPM = 12,819 - Rev Limiter W/Tune
Engine RPM @ 7,000 - - S/C RPM = 14,473

178mm Crank Pulley : 74mm S/C - - Ratio = 2.4054
Engine RPM @ 6,000 - - S/C RPM = 14,432
Engine RPM @ 6,200 - - S/C RPM = 14,914 - Rev Limiter W/Tune
Engine RPM @ 7,000 - - S/C RPM = 16,838

181mm Crank Pulley : 74mm S/C - - Ratio = 2.4459
Engine RPM @ 6,000 - - S/C RPM = 14,676
Engine RPM @ 6,200 - - S/C RPM = 15,165 - Rev Limiter W/Tune
Engine RPM @ 7,000 - - S/C RPM = 17,122

185 Crank Pulley : 74mm S/C - - Ratio = 2.5000
Engine RPM @ 6,000 - - S/C RPM = 15,000
Engine RPM @ 6,200 - - S/C RPM = 15,500 - Rev Limiter W/Tune
Engine RPM @ 7,000 - - S/C RPM = 17,500

Using a Stock Crank Pulley, the S/C pulley would need to be reduced to:

63.6mm to equal the boost of 178mm Crank Pulley running @ 6,200 Engine RPM
62.5mm to equal the boost of 181mm Crank Pulley running @ 6,200 Engine RPM
61.2mm to equal the boost of 185mm Crank Pulley running @ 6,200 Engine RPM

If 20,700 is the max S/C RPM; and to be safe we decide to stay 10% under max - that's a target of 18,630 S/C RPM - - (when at 6,200 engine RPM)

Stock Crank Pulley would need a 50.9mm S/C Pulley
178mm Crank Pulley would need a 59.2mm S/C Pulley
181mm Crank Pulley would need a 60.2mm S/C Pulley
185mm Crank Pulley would need a 61.6mm S/C Pulley

Check my numbers to see if I missed something.... because I want to replace my 74mm S/C pulley with a 61.6mm S/C pulley (16.78% smaller)