Update.
OK - I recently took the Thorens into my local dealer that usually does the work on turntables to fix a broken cuing mechanism, adjust the suspension and upgrade the interconnect cable. Turns out the belt I had purchased from another vendor was the wrong one, and I replaced that with the OEM belt as well. While in the shop I asked the technician's opinion about the combination of the TD 150 mkII and the Grado Blue cartridge. He said that it was a combination they often recommend.
Long and short, I decided to kept the Grado Blue for now and fiddle with set up a bit further. In place of the stock rubber feet, I placed a 3/4 inch thick Oak block under each corner of the plinth to support the Thorens above the the wooden platform it has been sitting on. I then adjusted the VTA from clearly too low to too high and back, finding the spot where everything just "snapped into focus". Horns blatted like real horns, guitar bodies resonated, voices reverberated, etc. - everything was "just right". The best I can describe this if you haven't experienced it is like the aural analogue of getting the focus correctly adjusted on a pair of binoculars.
This particular experience of a cartridge "snapping" into focus was the most dramatic of any of the other five or so turntables I have owned and gone through the same process with. The wooden blocks seem to have cleaned up a lot of stray vibrations and stored energy, allowing the cartridge to better do it's thing. The appropriate belt also had a big effect on timing, and now the platter starts without chattering up to speed - a big improvement.
So for now, I am very happy with both the table and the Grado cartridge. If I make a change for cartridges recommended above, I will report back.
