There are probably a hundred ways to look at this from overall economic growth in the market to population growth, to mix of platforms (radio, TV, billboard) in the market but I suspect at the end of the day what is really going to drive this is what a station, or a cluster will fetch on the open market.
Remember one key fact here: CBS is not GM. They aren't cash strapped and they aren't about to go bankrupt. The money realized in any sale will be used exclulsively to repurchase stock and shut up the Wall Street types who have been bashing the industry for the last 18 months.
They plan on selling 50, but that number could be in play as could the markets where they get out (remember the economy isn't collapsing at a uniform rate around the country. Some parts are hurting worse than others). Their dance partners are limited, there isn't much luquidity in the credit markets and the technology is changing by the minute. I would be suprised if they up and leave Pittsburgh entirely, mainly because of the TV. Don't be suprised if what they do at the end of the day is settle on moving 35-40 stations and ditch most of the AMs.