Tonearm for Cartridge Upgrade Path

The Denon and (especially) Koetsu MC's are low compliance types that need a higher mass, stable arm to play their best. The Clearaudio MM is a high compliance cartridge that will play best on a lower mass arm. IOW, the arm that works best for the MM won't be the arm that works best for most of your LOMC choices.

Which way you should go is up to you, but if you plan on using the MM and the MC on the same arm, you'll have to compromise one way or the other.

My choice would be to optimize the arm for the more expensive cartridge. It seems to me there's little point spending $2-4K for a cartridge if you're not going to get the most out of it. If the less costly MM doesn't play quite up to its best, oh well...

I have a wood bodied 103R currently in a Premier FT-3 on a Gyrodec.

I frankly don't see the need to go beyond the wood bodied 103R; my educated guess is that the Miyabi/Koetsu/Shelter upgrade path would be a heavy situation of the law of diminishing returns.

My tonearm upgrade when I do it will be to one of the following:

Used SME 309, used SME IV, or Thomas Schick with the IV and the Schick being the primary candidates and the 309 being a "settle for" option.