It really makes no difference whether the cart is 36v or 48v if it is running with a controller.
The biggest difference is between resistor carts and controller carts, resistor carts have a shorter run time. The resistor cart is much simpler n design but the controller cart is a much more efficient use of available power.
A controller cart varies it's speed and power by the application of the throttle and supplying power when it's required.
A resistor cart basically applies full power all the time and is regulated by the number of resistors across the power supply.
The difference between the two is like driving your car with the throttle to control the speed (controller) vs driving your car at full throttle and controlling the speed with the brake (resistors).
IMO, if you are satisfied with the speed and power of your cart and simply want more run time, it would be less expensive for you to convert your cart to a 36v controller. If you need more speed or power, have the motor rewound for the purpose.
With a lift and large tires you should consider using a controller that is at least 400amps.