I think that 3/8" tooling is the max that really matches the capability of the machine, and most of the applicable larger diameter wasteboard surfacing bits and bowl bits come in a 1/4" shank. The C3D/Makita collets as @WillAdams pointed out can run a 3/8" collet, as I have and it works great. In my opinion and experience, 1/2" tooling is the area of larger machines anyway. 
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