Koetsu Jade v SPU classic v FR 7 fz cartidges

Greetings to all !
I am hoping to get some advice concerning my analogue set up.
I use a Brinkmann La Grange turntable with a FR 66s tone arm.
I bought the FR 66 as a high mass "match" for my Koetsu Jade cartridge which has just been fully rebuilt by Koetsu with diamond cantilever.
The rest of the system is Allnic H 3000 phono stage , Allnic L 5000 line stage, Aklnic A 6000 monoblocks and Quad 2905 speakers / Audiophysic Rhea 2 subwoofers (pair).
I listen to a lot of choral classical music and for this the midrange needs to be really " organic" and free from any harshness or glassiness and , very importantly, the cartridge needs to track demanding loud and complex passages properly.
In this latter regard I am not 100% convinced by the Koetsu. It has been professionally installed in the FR 66 using proper alignment tools and is mounted in an Orsonic headshell. Yet to my ears it gets " nervous" in certain demanding passages of music .
I have tried increasing the VTF to 2.5 grams (the maximum recommended is apparently 2.2 gm ?) and this does seem to improve things but I assume that this will have som negative effects given it is some way over the " limit".
I just bought a " standard" SPU Classic (with spherical stylus) in the integrated headshell and, tracking this at 4 gm, I was instantly bowled over by the " organic" midrange in the type of music referred to above.
After a series of "A/B" comparisons with the Koetsu I am struggling to say I really prefer the Koetsu to listen to in my system , although it clearly has greater frequency extremes, transparency and detail than the basic SPU ( it costs over ten times as much !!)
I was wondering if anybody out there has had similar experiences with Koetsu stone bodied cartridges ?
I am now thinking of going for one of the FR 7 cartridges ( fz version) and again would welcome any comments on this and how it might compare to the Koetsu / SPU ?
With kind regards,
Howard