@noromance
I would describe the improvement of the AF idler wheel as similar to a cartridge upgrade - the higher frequencies were more detailed, more nuanced. There were also improvements in coherency and musical timing.
When we upgraded to the Artisan Fidelity idler wheel, the 401 had already been refurbished by Audio Grail, in other words the AF idler replaced a refurbished standard idler wheel in good condition. The 401 in question also had had an upgraded platter and bearing from Peak Audio which had yielded a massive ( not hyperbole ) improvement in musical timing.