the only issue for me is the Arrowspeed budget tyre vs the other 3 premium brands, Is it worth relegating the Arrowspeed to the role of spare tyre?
Not a bad idea at all, of course depending on the presence of a full size spare.
In my experience, many of the cheap Chinese tyres do not age well, but seem to fare better hidden in the boot away from the UV. On the car, they perish and crack quicker than many - watch out particularly for cracks in the root of the groove treads around the tyre... particularly nasty. Modern tyres have a very thin cover of rubber over the steel plies, and they can soon be exposed.
I wouldn't recommend them for low mileage drivers, you end up swapping them with plenty of tread left, especially on the back if you don't rotate. Avon/Cooper tyres (same factory) also seem a bit duff in this respect, I've swapped a couple of Avons for cracking, and the 4 brand new Coopers that the other half's Jazz was shod with when purchased are already showing signs of age.