I put my Nankangs on mid November 12' and took them off last week of March.
I could barely see any wear to the naked eye apart from the original 'brand new' pattern having worn off of course. For £198 for two tyres I thought that was awesome value, personally. There must be at least another two winters in them, possibly more.
I did the same and they were totally bald when I took them off! Crap tyres. I'm splashing out and trying Continental TS830P's this year...
edit: after looking at some pics, mine were SV1's. Still crap, though!
How many miles is that Si?
Bizarre, really. Mine were barely caressed by the road and I'd have done around 5,000 miles in that time, maybe a little under. There's between 6.5-7mm of tread left on both I'd say, comfortably.
The SV1 & SV2's can't differ that much so it must be our driving styles that differ