Alexc, my experience was brief with the SME 20, and the system not fully familiar, but my feeling on it was that it was pretty much on the same level as my Basis (an Ovation which has been upgraded for all intents and purposes to a Debut Mk. V vacuum), but not an improvement. I preferred the sound of a Basis 2800 in that system marginally (felt it had a "blacker" background), but part of the difference might have been in the Graham vs. SME arms as well. The SME 30, on the other hand, which I heard on a number of occasions in a more familiar set-up, did have an ease and naturalness around it that seemed a level up from my Basis.
I can't add much more to Albert's excellent post; I too use a Walker motor drive with my Basis, principally because before the upgrade I had to change the pulley spindle each time I wanted to change speeds, a genuine pain in the rear (since the upgrade Basis now has a two-level pulley spindle, so I technically don't need the Walker for speed control, but it works so well at cleaning up the sound I've kept it). If you can contact Lloyd it might be worth it, as he may be able to make a custom model for you.
I can't add much more to Albert's excellent post; I too use a Walker motor drive with my Basis, principally because before the upgrade I had to change the pulley spindle each time I wanted to change speeds, a genuine pain in the rear (since the upgrade Basis now has a two-level pulley spindle, so I technically don't need the Walker for speed control, but it works so well at cleaning up the sound I've kept it). If you can contact Lloyd it might be worth it, as he may be able to make a custom model for you.