About a 15 or 16T would get you where you want to be. I'd go with the 15T if it were my vehicle.
Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 48
Pinion Tooth Count: 15
Total Voltage: 14.8
Motor KV: 2084
Tire Diameter (inches): 4.5
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0.0073
Spur/Pinion Ratio: 3.2 : 1
Total Ratio: 10.58462 : 1
Tire Circumference (inches): 14.14 inches (359.08 mm)
Total Motor Speed: 30843.2 RPM
Vehicle Speed: 39.01 mph (62.66 km/h)
Effective Speed Rate: 2.64 mph/V (4.23 kmh/V)
Estimated Adjusted Speed: 37 mph (59 km/h) - 5% loss
Effective KV Value: 2084
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...
Also, go here to do your speed calcs...
http://www.scriptasylum.com/rc_speed/_top_speed.html