I have a 150mm lens and a 63 mm lens. The 63mm lens only allows me to engrave, or cut, a very small area. I almost never use it other than just playing around. The only reason I put the smaller lens on, is to send more power to the part I am working on. 110 to 200 is a good range of lenses to use on anything with a 60 watt. If anything, I would want a 300mm as well. And that is just for 1- A larger work area. 2- And most important, Better results with a curved or wavy material.

You will loose some power close to the very edge of the lens. Not much in most cases. But, it is best to try to keep the work centered as best as possible.

With a 300mm lens, you would also need a tall tower to get it in focus.