Bazza.......I've used SO2's on a standard turbo Impreza (16 inch wheels) and on an Impreza RB5 with Leda suspension and the standard 17 inch wheels. The first car's tyres were fitted with the SO1s, but when the SO2's where fitted the level of grip especially in the wet was quite remarkable in comparison. I had P Zeros on the RB5 initially and changed for SO2's and again the wet grip in particular was considerable better, the dry grip pretty similar. For what its worth I'd say the RB5 (with SO2's) had more grip than my VI with SO1's.
I too will be on the look out for new tyres on my VI shortly and my main gripe with any road tyre is the speed in which the outside edges of the tyres wear out compared to the middle and inside. Even with serious amounts of camber on the front, the edges eventually start to loose chuncks out of them (as with the VI after only 5,000 road miles). Consequently I will be considering the new Pirelli P Zero Rosso tyre against the SO-2, quite simply because the SO2's are quite soft and in my experience the shoulders soon wear flat. The P Zeros have a flatter profile at the edge, and the outside rubber seems to be of a much harder compound than the middle and inside of the tyre. Furthermore I found the P Zeros less likely to tramline and less fidgety under braking, and certainly created less road noise. However I do think that the SO2's are unbeatable in the wet, and that's what make the decision so difficult. Whether there are any other tyres worth considering I cannot say.
Steve