Dean Baker reasons that 10.5% is about the minimum to expect for year end 2009:

Even if the economy, lost no additional jobs between April and the end of the year, then the unemployment rate would still rise to about 9.5 percent by December. If it loses 1.6 million jobs (200,000 per month), then the unemployment rate will be 10.5 percent by December. At this point, this is probably about as optimistic a scenario as can be believed.

So, if a job loss rate of 200,000 per month through year end and an ending level of  10.5% is optimistic, then a job loss rate of 400,000 per month through year end would result in 1.0% more unemployment than 10.5%, or a 11.5% level at year end.