I agree with Lewm and Billstevenson on loading based on practical hands on experience using both; the SS Hyperion MK II and new SS Hyperion MK II MR.
I initially loaded the Hyperions’s per the manufacturer’s recommendations and not long after discovered through listening that changing the loading increased listening pleasure. From my observations, I heard better resolution and less midrange shoutiness, or excessive peaks…it seemed to balance out and improve performance with these changes in loading.
My process to come to this conclusion is somewhat similar to how you started. I initially started at 400 ohms and then did a giant leap to 47k ohms. This was to interpret gross performance differences between the two loading ranges. After experimenting with those two loading ranges, I opted to try 1k, 4.7k, and 10k. I also dipped down to 243 to see what sound differences I could discern. I have an Aesthetix IO Eclipse phono stage with dual power supplies which allows for those loading values. I actually can go as low as 10, 20, 40.2, 75, 121, 243, und weiter.
The realization is that I was able to come to the final loading ranges based on experimenting with the different loads my phono stage allowed me to use. I arrived to the 47k range after listening to all the other loads and concluded that 47k was perfect with the two different Hyperion models. Always take the manufacturer’s loading range as a starting point and experiment through listening and alternating between other loading ranges to get the best balance in sound.
I do not find the Hyperions having any peaking attributes on the high end with 47K loading. I have an Air Tight Opus 1 which I do find to be more restrictive to the manufacturers loading range; however, that cartridge is a low output MC cartridge and not the same type of construction as the Soundsmith cartridges. I only mention this as once you acquire various cartridges and experiment, you too will come to similar conclusions. Have fun listening.