I have an Aeron chair and the casters that come with it are not that great. I use it on a chair mat but it still not very smooth to move around. I don't think it is my chair mat because it is supposedly a high quality one (1/4" thick, cost me like $150). So there are two other caster options offered by Herman Miller: a / Deep carpet casters. These are the same material as I currently have (plastic) but they are slightly larger and looser to allow for more free movement. b / Hard floor casters. These are the same size as my current ones, but have a rubber coating instead of plastic. See a description of all three: http://www.aerons.com/casters.html?hs340=rightnav_Caster_Options Which do you think would offer better performance? The customer service rep from Herman Miller said that sometimes the plastic casters can be a problem on a chair mat because plastic will stick to plastic. But a chair mat is not really a "hard floor" as in hardwood or tile, so I don't know that the rubber ones would be best. I know there are a lot of intelligent, analytical people in these forums so please help me decide which would improve the situation the most.