We survey hundreds of UK and US operations each year, and stats like you ask for are available in the US Contact Center Operational Review. The 2009 edition is coming out later this week (title: US Contact Centre Decision-Makers' Guide), so please watch out for that.
I currently Manage a 45 seat center for Pest Elimination Co. (Comercial Services). Our ASA is 15 seconds with an SLA target of 85% answered in 30 seconds. Our Current abandon rate is 2.5%. Solid business model, sound cost structures along with carefully managed and forecast revenue flow combined allows us to accurately staff for target SLA's.
I previously co-managed a 300 seat Tech Support multiple site center (Comercial Services). Our ASA was 80 seconds with an SLA target of 90% answered in 45 seconds or less. Our abandon rate was 11%. Restrictive and complex business model, complex cost structure along with highly restricted revenue flow (Contractually) and forecasts made it very difficult to accurately staff for target SLA's.