The High Speed Gears will give you a nice increase in top speed but you'll lose quite a bit of torque. If you use the cart for street cruising on level ground they work great with the stock motor and controller. If you don't have at least 4 guage cables I'd consider upgrading them with the high speed gears.
A EMP motor will give you about the same top speed as the gears without loosing all your torque. But your looking at about $100.00 more than the gears will cost.