I have a lot of experience wheeling around "dead weight."

I can attest that the best casters for anything in the shop are medical casters like the ones on hospital gurneys. They are made to handle a lot of "dead weight" and are extremely solid and smooth rolling.

Imagine the daily routine of a caster on an ambulance stretcher...

Pick up 500lb man and roll through 50' of front lawn onto the gravel driveway... Unload at the asphalt parking lot at the hospital. Roll over the threshold smoothly. Roll smoothly into the ER. Get a little bleach splashed on you. Repeat 10-15X daily for 5 or 10 years before you are replaced. Oh, and expect a half million dollar lawsuit if one ever breaks.

These things are STRONG.

http://www.humphriescasters.com/catalog/bedCasters.pdf