>>Has anyone compared recent linear and pivot tonearms on a 2-arm TT at the same time w/ the same cartridge for an A/B comparison? What did you notice?<<
As I wrote earlier, the Souther Linear Arm was designed to work well with a wide range of phono cartridges, including the low-mass, very high compliance ADC XLM series -- which were designed for for 0.5g tracking force. During the final couple of years of refinement of the Souther design, I did listen to a variety of Souther prototypes and then final production on a Luxman PD444 turntable while a variety of pivoted tonearms were simultaneously mounted on the turntable. A/B comparison with the same model cartdrge was routine, made easy by the two-arms-to-one-source switchbox built into the underside of the Luxman. No, this doesn't qualify as "recent." Pivoted tonearms in rotation were Grace 707, Transcriptors Vestigal, SME 3009, Mayware Formula IV, Infinity Black Widow, and occasionally we had access to a friend's Dynavector 501. A variety of other tonearms passed through our hands for shorter-term audition, including the Signet XK50 and some pretty good Japanese S-arms sourced from dead direct-drive turntables as well as relative exotica like the KMAL.
The striking thing about linear tracking vs. the pivoted arms was the absence in straight line tracking of a subtle "fuzz" that couldn't be tuned out of any of the pivoted set-ups. We certainly tried, painstakingly aligning every tonearm. But in comparison to the Souther linear tracker, pivoted arms that sounded incisive in transient detail outside comparison were made to sound comparatively compromised by subtle blurring of transient clarity. The linear tracker snapped everything into sonic focus that you didn't realize was available until you heard it. Other comparative differences varied by tonearm, though the Souther did consistently also present the 3D soundspace more vividly than did pivoted arms, and to our ears it sounded tonally the most neutral, consistently.
My primary long-term comparative testing of the Souther vs. pvoted tonearms relied on a handful of cartridges, primarily ADC XLM II, Shure V15 III and IV, Denon DL103D, Supex 900, Grace F9R, Adcom CrossCoil. We particularly ran ADC XLM's into the ground in an attempt to show that linear tracking in the Souther would be too stressful to that cartridge's delicate cantilever and suspension. They generally fared worse in the pivoted tonearms. Over two years we couldn't find any evidence of the Souther arm wearing out the XLM sooner than a pivoted tonearm, though the test wasn't scientifically rigorous.
My experience using Souther production tonearms over the next ten or twelve years bore this out. That tonearm is at least one instance of mechanically-coupled passive linear tracking imposing no penalty on cartridge life despite the only lateral motive force being that imposed by the spinning spiral groove, with the cartridge stylus, cantilever and suspension being the means of transmission.
Phil