3 lbs. of paint is a LOT of paint for a model of that size, even if you use a two stage automotive type paint. You should not add more than just a few ounces when painting a model of this size. Any more and you are applying the paint way too thick. Remember, you want only just enough paint to provide even coverage. Any more than that is a waste of paint, money and weight.

To your original question though. If you end up over weight on your model, you can expect it to have lower performance in climbs and handling than if light. It will not respond as crisply, or smoothly as it would if built light. As stated by others, it will both take off and land faster. Faster landings are harder on the air frame and landing gear in particular. You will also have to fly with more power which means the engine has to work harder and uses more fuel. Prop choice becomes more critical as you need to choose one that will fly the model fast enough to be comfortable in the air, but this usually means a sacrifice in pulling power for take off's and over shoots.

John