Which Mono Cartridge at around $1,300.00?

I'm in the process of upgrading my well cared for Thorens TD145. I started by soldering in WireWorld phono cable along with getting a basic tune up. I want to replace my Grado ME+ mono cartridge with a substantially better mono cartridge. Currently, the tone arm is stock. My records are classical (orchestral, chamber, vocal, etc...) dating from the 1940's and 1950's so I've been cogitating on the Ortofon SPU Mono GM MKII or a low output Grado (i.e. the sonata reference 1). My phono stage is the ASR Mini Basis Exclusive. All or any suggestions would be greatly appreciated.
Thanks!