No... The balance to be made is between torque and speed, making your gear reduction half what it would otherwise be will slow you to a ridiculous extent as your acceleration would be hopeless. 'Horsepower' doesn't really matter, it's just a hint at torque/speed characteristics which you should be designing around. The best thing is to use the tentacle calculator to try some gearing combinations with a motor similar to yours, and enter a realistic tire coefficient then you can click the 'acceleration' button for more information: http://www.architeuthis-dux.org/torquecalc.asp