You made a great choice for motor on 6s, I tryed a setup using a 23 tooth pinion using BrianG's calculator
Differential Ratio: 2.8461538461538463
Transmission Ratio: 1.8333333333333333
Other Ratio: 1
Spur Tooth Count: 65
Pinion Tooth Count: 23
Total Voltage: 22.2
Motor KV: 1516
Tire Diameter (inches): 5.9
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0.0138
Spur/Pinion Ratio: 2.83 : 1
Total Ratio: 14.74638 : 1
Tire Circumference (inches): 18.54 inches (470.8 mm)
Rollout: 1.26:1
Total Motor Speed: 33655.2 RPM
Vehicle Speed: 40.06 mph (64.35 km/h)
Effective KV Value: 1516
KT constant: 0.89 oz-in/A
If you use a 22 pinion, you'll be around 37 and with a 24 you'll be at about 42mph, here is the link to the site if you want to try some different setups.
http://www.scriptasylum.com/rc_speed/index.html
BTW, Welcome to the forums