Well, the first pass was completed -
Premier Ink supplying Print-Rite cartridges.
I had 4 cartridges - Black (small, for colour printing), Cyan, Magenta and Yellow, of which all but Yellow were Print-Rite, while the Yellow was Canon, as a "control".
Interestingly, the 3 Print-Rite cartridges have all expired, while the Canon is still going strong. Obviously this is far from conclusive, but it does suggest that the 3rd-party cartridges don't have the same longevity as the original Canons.
The original Canon Black (large, for B&W printing) is still going, also.
In terms of colour quality on test prints, my view is that the replacements were slightly - but perceptibly - paler or washed out compared to the originals, although the black was indistinguishable. In real-world printing there's very little to choose between them.
I've now got a set of Tesco cartridges to compare. Results in a... while!
SD