Clearaudio Outer Limit on SME 20?

Hmm, if you are using the SME clamp right, with the washer, and put the right amount of torque on the clamp, the outer edge makes contact with the platter.

Of course actually trying the ring may yield a good result.

I'd think SME would have given this a go over the years and offered one if it makes a difference on their tables...

Same bearing as in the larger SME 30, which has a much heavier platter, so no, no damage. I have a Bob Benn clamp for the SME 20, but that can be used with any table whose platter does not exceed the diameter of the record. I found it gave a much more stable, deep soundstage than without and eliminated any vestiges of vinyl resonance. I have an SME 30 now that it doesn't fit, so I will be selling it.
On the SME 20, the spin up time is not particularly effected and the clamp weighs about 4 lb.

Will the clamp fit an SME 10 table?

The Benn clamp is centered by the record itself, it has a lip for this purpose. The SME 10 platter is just slightly larger than the SME 20, but less than the 12 inch diameter of the LP, so it should work in theory. I haven't done it, though, so it would require actually fitting it to know for sure.
I have never used the Clearaudio clamp, but it fits on a SME 20 so should also work with the SME 10, but requires a centering jig, as I understand it.