I've seen other posts where people are estimating a 20% - 25% increase in performance, but to me that's just a pipe dream. The 10% increase is a more realistic estimate.
It really depends not on just what happens to the chip, but also what improvements AMD can get Microsoft to implement.
Techreport did an interesting wright up regarding Bulldozer and Windows Thread Scheduling
While somewhat limited in scope, they found that by manually scheduling threads they could obtain 20% better performance vs Windows scheduler in select applications.
While performance increases like this will probably not effect people like OP who constantly peg all eight cores, it is something quite interesting to keep in mind before automatically dismissing 20-25% performance increase claims.
That said, unless either Microsoft decides to patch Windows 7 or AMD changes how their cores are reported to Windows (taking a hyperthreading 1 core 2 thread approach, which is doubtful as it would kill their '8 full core' marketing
), I personally believe a 0-5% IPC increase to be more realistic.