Fidelity Research 64s vs Jelco SA-750e

I owned both the Jelco 750D (9-inch) and the FR-64S played with my RSP. The Jelco was tweaked with the old TTW VTA collar which, like the B-60 base, adds even more weight to the arm. The FR-64S was without the B-60 Base. Head shells were Yamamoto HS-4 (Carbon Fiber), HS-6 (Titanium) and Ortofon LH-8000 (Laquered wood).  
In my system, the overall difference was small with the edge going to the FR-64S.  The FR with the LH8000 had the best combo of bass extension, midrange beauty and extension on top. Perhaps the difference would have been even greater with the B-60 base but it was enough that I was happy to sell the Jelco and do not miss it. I think the difference is small enough that you can take your time to find the right FR-64 (condition wise) for your table. 

Though I haven't had a stock 64S base, I'd agree with chakster that the stock 64fx base is really nice and solid. It's also very easy to dial in VTA with this base - not as easy as with a true VTA base, but easy enough unless you like to change VTA between records. 

This is great feedback! Exactly what I had hoped for. Karl_Desch, what a break for me that you have experience with both of these with a  Koetsu. Thanks so much.

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.