Glyn - my chain was regularly tensioned, lub'd etc and developed tight spots etc just before the 12k service. It seems from all the posts that that is about the distance for a chain on the ST series - mine's an ST4s.
At the time of changing I had a Renthal 15T front sprocket fitted and a std rear, plus the Tsubaki 102L chain - total bill = £126.74
Hope that helps.
