Carbs aren't nearly as efficient as fuel injection, however sidedraft carbs can come very close when properly tuned. With carbs, you're going to lose precision in controlling the mixture.

Think about it like this, with a carb you have a "dumb" mechanical device with no feedback loop metering your air/fuel mixture. As a result, you will have to run slightly rich to make sure that you never encounter a lean condition.

Fuel injection on the other hand, will allow much more control over the engine's operating parameters. There are electronic sensors providing feedback to the ECU. The ECU is then able to optimize the amount of fuel being delivered for the desired power output. A by product of this is better fuel economy on a properly tuned vehicle.