It sounds to me like you really like that Thornes table after all the work you have put into redoing the plinth. Any tonearm would be a huge up grade over that TP16, so I would throw a different tonearm on it and keep it. The RP6 is a great table for sure, and you can upgrade it as well. Either one you use, you will up grade. Your choices for cartridges in the future should be considered, the Rega will play well with most med compliance whereas depending on the tonearm you use on the Thornes you could use a Higher or lower compliance one. Also, I found the Grado reference Sonata woodbody to work very well with the TP16 tonearm for what its worth.
Matt M
Matt M