Sestak probably beats Toomey by a couple points; Toomey probably thumps Specter by 5 or more. I know all you Democrats think Toomey to be a nut, but as someone who actually lived in his district for a handful of years, he comes across a lot better and a lot more electable than you think...
I've lived in PA 15 for a while as well. I didn't exactly think that was a conservative enclave, but Toomey managed to win tha area for years and that says something. Union Dems are tired of Specter's sh**t and may revert to Toomey by default or not vote at all. Sestak OTOH is more electable upstate and out West due to his background.