Laser Engraver Forum

I am building a machine based on the plan from FurtherFabrication. I am looking at a 130w tube. It is available in both 65mm and 80mm diameters. Someone said that 80mm is recommended, but can't explain why.

I know that the 65mm is cheaper and has a somewhat shorter lifespan, but what is the real functional difference between a 65mm tube and an 80mm tube?

Thanks.