Fidelity Research FR-64 vs. FR-54

It seems like even black 64fx is not so popular as 64s, i wish to know what's the difference between them?  

The FR54 is a much cheaper tonearm, so i assume it's not on the same level as 64s, not even close, right ? 

I've never tried. 

Haha! 
You're probably right, 2channel.  I plead guilty to letting the exchange degenerate into a mano a mano.  However, someone wrote very early on that the FR64S is generally considered to be far superior to the FR54, and I, for one, assumed this is a given.  The FR64S/66S were Fidelity Research's best efforts, along with the fx versions of the same tonearms.  Most end users also have written that the FR64S is superior to the FX version, by a wide margin.  I cannot attest to that, either way.  

With any tonearm capable of dynamic balancing, it is usually not imperative to use the dynamic mechanism; one can optionally achieve the desired VTF by re-positioning the counter-weight, just as with any tonearm that lacks dynamic balancing.  Among those who have an opinion, dynamic balancing is controversial.  One would have to try it both ways with any particular combo of tonearm and cartridge.  I do use the dynamic balance with my FR64S, largely because the Acutex cartridge is so light in weight that I cannot otherwise achieve VTF.  I looked around for a heavier FR counter-wt, which would make it possible to balance the tonearm mechanically, but did not find one.

Lewm

I do use the dynamic balance with my FR64S, largely because the Acutex cartridge is so light in weight that I cannot otherwise achieve VTF. I looked around for a heavier FR counter-wt, which would make it possible to balance the tonearm mechanically, but did not find one.

This don't make sense, if the Acutex is too light you would need a lighter counterweight. Most people have the 250g counterweight with the FR64S.
I have the W170 ( 170g ) lighter counterweight which is useful for lighter cartridges; you should try and get hold of one if you are going to use a variety of cartridges on your FR64S.

Dover, Your logic is impeccable. My memory was not, and anyway I should have thought more about what I wrote.  The actual case is that even with a slightly lighter than OEM headshell and even with the Acutex (lightweight) cartridge, the CW is very close to as close as it can get to the pivot, with the assembly just balanced horizontally, at zero VTF.  So I then used the dynamic to dial in VTF.  If anything, I need a lighter CW.  And your post reminds me that I did look for the W170 on eBay and Audiogon but have not found one.

I do in one sense like it the way I have it, because having the CW as close as possible to the pivot is a virtue in terms of minimizing effective mass, in view of the high compliance of the Acutex.

I suppose that to make a light CW heavier, you could also use those lead weights that are normally used in wheel balancing.  They would tape right up against a cylindrical CW, like the one on the FR64S.