Twl,
It's refreshing to hear from somebody who is so aware of the realities of physics in analogue: mass matching seems to be something of a forgotten art these days. This being so, I thought that some clarification of your point was necessary for Joeljoel, to wit, that the cartridge mass must be added to the tonearm mass to come to a total system mass for the calculation to be meaningful. Just because jj knows the mass of his cartridge, doesn't mean he knows to add this mass to the mass of the tonearm (no slight intended to jj).
The point concerning my Decca is that the Shelter is a low-compliance cartridge, and for this reason feeds a lot of energy back into the tonearm, as Dougdeacon noted. The Decca is the lowest compliance cartridge made, thus feeds back the most energy, and so provides an example in practice of unipivot/low-compliance matching (the Decca is a bitch to match to anything). Dougdeacon provides the most relevant information of all, actual examples of such matching with a variety of unipivots. Since jj seems to favour the unipivot (I know not why), then I thought I would encourage him, I have no agenda, and actively use a variety of tonearms, including a modded Rega, a knife-edge bearing, an air-bearing, and so on. Had he favoured the modded Rega, then I would have told him of my good experiences here.
I would add something to Dougdeacon's detailed expose, however, that very few combos can track the cannons, and the HFN testrecord is increasingly considered as an unrealistic test of a cartridge-tonearm combo. In practice, "real-world" records, which is to say regular commercial pressings, rarely present a problem. But nothing is perfect. To get back to my Decca (only one of my many cartridges), there are quite a few things it will not track well (except in one tonearm I have tried), but I love the sound and so learn to live with it. It's just plain a blast to listen to. For this reason, I keep other cartridges around, like the track-everything Shure V15. Perhaps jj just wants to have fun, too. But the Shelter should be quite a lot easier to live with than my Decca.
By the way, in getting back to the person who is asking for the advice, why do you lean towards the Unify, Joeljoel?