I bought a second Sprint St a few months ago (do 300 miles per week) and put Storm's on straight away (azaro st's on my other ST, which has done 72K miles, mainly on Avons). The Storm didnt have that off the line wobble the Azaro's had, they live up to Avon's claim about grip, mileage and stability (so far). Worth the extra - probably, I liked the Azaros and the Storms are every bit as good but I doubt I will explore the improved aspects of the new tyres, except I did notice the rear seems to be worn to the out edges and I dont recall the Azaros getting over that far

I'll be putting a new set of Storms on when these need replacing though. A couple of things I noticed about the Azaros, a new set hardly changes the handling from an old set (most odd) but they are much better than Bridgestones when they get old and a bit squared off, the handling hardly changes at all, unlike the Bridgestone which go off before they are truly worn out. All in all I prefer the Avons, maybe the newer Bridgestones are better than the old but I wont be changing away from Avons, they inspire confidence, wear well and cost a bit less too.
Matt