always did pairs (rears first) - until last tyres change, when I swapped the whole lot (including two good rears @ about 5mil each) for Toyo Proxes.
I had heard nothing but good things about the Toyos, and the rate I was getting through the potenzas was becoming very expensive (near £700 for 4 new potenzas, and then 7k later, 2 new fronts, then 13k 2 more fronts

)
touch wood, throw salt over his shoulder etc etc - the Toyos are wearing well at over 10k with no sign of abnormal wear despite some time with tracking seriously out