Fidelity Research 64s vs Jelco SA-750e

I haven't made a move on tonearms yet, and instead changed phono stages from my ear 834P to a Joule OPS-1. I had Rich at Signature Sound upgrade caps to Jupiter Copper/wax and he also improved power supply. My God what a fantastic component! I cannot believe how organic, non-fatiguing and magical it sounds. Everything is a notch better in terms of convince people and instruments in real space. By the way, Rich was so great to work with. Super conscientious, careful and his work is beautiful. A+ for him!

So back to tonearms... Does anyone have an opinion about how much better the FR-64x or 64s might be than the Jelco 850? The 850 would be a drop-in replacement and no worries about weight with my aging Sota. I will either get the 850, or, if the FR arms are significantly better, wait and upgrade the table to a Nova or Cosmos and get an FR arm down the road a bit.

Thanks
Stu

As I said above, the 850 is significantly better than the 750. Jelco now make a 10" 850M. The 850 is open and transparent. 

Yes I have no doubt, basednon your and others' comments, that the 850 would be a great upgrade. I am just wondering how much I would be missing by not going all the way to a FR arm. I kinda feel like I might get 80% of the benefit by going to the 850, in which case due to cost and hassle, the 850 would win.

 @noromance I am getting a quote for the 850 M to go on the recently back from rebuild at factory Saphire. The Ft-3 that came with it is shot...

Not exactly sure what cartridge..yet...something below $2 K

I bought a used Koetsu Rosewood Signature for $1400 that I use with my Jelco 750e (10") and old star.sapphire and it is pretty amazing sounding. I have trouble envisioning how it could improve, with the exception of perhaps less groove/record noise. But  buying used cartridges is high wire work... A little scary. I got lucky.