I believe that a cartridge and a speaker, by far, contribute the most to SQ.
I would dispute this assumption.
In my view the TT trumps all. I'd rather have a the best TT I can buy with a $500 cartridge than a top cartridge with less than optimum TT.
In your case a tonearm upgrade would arguably unleash more performance than changing cartridges. I currently have a Garrard 301 with FR64S in my B system and have set up many arms on Garrard's including Moerch, Helius, Kuzma to name a few. Each of these arms offers a different perspective on any given cartridge.
I have owned or set up most of the cartridges you mention -
Personally I prefer the top Soundsmith MI's to their strain gauge.
The Decca MI's are superb, but can mistrack unless perfectly set up in an appropriate tonearm due to the lack of suspension. They are now out of production.
I also have owned a few of the cantileverless MC Ikedas from the 80's - they are the MC equivalent of the Decca.
Current favourite of current production cartridges would be Van den Hul Grand Cru which I have recently set up on a Kuzma 4Point11.
The reality though is that cartridges are so dependent on TT, tonearm and phono stage interface that they can only really be judged in the context of the supporting components, and the best cartridge is the one that works best with your particular arm and phono stage.