If you give up your Garrard 401, my guess is you'll find unsatisfying the comparative lack of drive in the other turntables you mentioned. There are two meaningful upgrades you can make if you're inclined to make improvements: 1/ Abandon the granite plinth in favor of either slate, or a Shindo-style layered hardwood alternative. Both will sound different from granite, but significantly better, sonically. 2/ The SME 309 is a well-made tonearm but not ideal. In upgrading your plinth you could also build for a 12" tonearm or both 12" and 9", with a change in cartridges to better extract the tone density possible from that turntable. Of course, the tonearm choice will be affected by your cartridge preferences, and vice-versa.
Phil
Phil