The SL1200 is more speed stable and I think the plinth is more sorted out than all the SP-10s and that includes (at least for now) the new SP-10R which is supposed to be released soon. I would expect the SP-10R to have state of the art speed stability. IOW unless you are willing to devise or otherwise find a competent plinth for the SP-10 so that the arm can be properly mounted, you might be better off with the SL1200G/GAE.
Funny how Technics manages to get so many things right then there's that one glaring flaw that has you scratching your head... In the case of the 1200 I think the platter pad and the arm are the weak links, although the arm is much improved and totally takes on many high end arms.