Fjn04,I had two different stone body Koetsus.Loved them!I cannot see any reason for the Phantom(new or old) to have any problems with either.
The heavier counterweight would allow for the weight to be a bit closer to the bearing,but I cannot possibly see any reason for the older weight to not be fabulous.We all get a bit carried away with minutiae,in this hobby at times.
I'll bet one would really have to strain to hear the difference between the older Phantom and the newer one.
What happened with me,at my pal's home(he owns the original Phantom)was that we decided to get a bit nuts with the damping fluid,as we both owned the 2.2 awhile back.THAT arm is incredibly sensitive to fluid!The Phantom is not as sensitive,but it is still VERY critical of it,with the Orpheus cartridge.
So,we played around alot,and lowered the amount of fluid to the point of about half as much as previously used,as per Bob Graham's recommendation(that particular week,two months ago).
Of course he had gone from the Kharma 1.0 to the Magico Mini,so the different voicing of fluid was probably affected by the different personality(timbral/harmonic....and GORGEOUS)of the Magico Mini.
Needless to say,he is in audio heaven,as of now,and is not all bent out of shape about a micro improvement(if any),to an already great arm!
LP's we used for comparative results were Bang Baroom and Harp(RCA),Tabooh Tabuhan/The Black Maskers(Mercury 1s pressing),Decca Lp of Prince Of The Pagodas,Frank Sinatra Swingin' Session(capitol),Pop Pop/Ricky Lee Jones( re-issue),The Pendrecki Partita for Harpsichord and Orch.(EMI box set,and dynamics to die for)and a load of various violin cto's/solo stuff from Ida,Itzhak,Erica to "you name it"(my friend is a violin "maniac",and has about every violin disc ever pressed.Too many,IMO,but it's his money(he's probably spent more money on violin discs then his system)......BTW,theTransfiguration Orpheus is amazing with this arm!
Best.