Hi Lewm,
IMHO, the Rockport is really an integrated engineering marvel.
As you know, with all tonearms there are some cartridges that are just a better fit than others; otherwise, just as Syntax mentioned above, it can be a very risky endeavor when running a light VTF Olympos with the Rockport tonearm. The previous owner from whom I purchased the Sirius lll, did crash his Olympos and the cartridge required a roundtrip air-lift flight from the Seattle area to Lyra for rehabilitation...no, no, no...
...now, there is this wonderful audio chap that I know that is just really MAD about the Rockport turntables. He is building an audiophile's basketball team and needed to finish out his starting lineup...a Tex Winter Triangle Offense.
...so he now has 3 lll's, and 2 ll's...a glorious starting 5 for Team Sirius! Well, there is also the rumor of a possible one-off V.
He prefers the Koetsu Stonebodies and Goldfinger cartridges interfacing the groves with his Rockports; he tells me there is no latent hop, skip, and/or jump problems with these hold-me down babies.
Lewm, I hope this helped!
Best,
Alan