Single core performance has been pretty much stagnant for years, anyone with a dual core or quad core system should theoretically have much better performance than a new top of the line CPU that is artificially limited to 1 thread.
Yes, theoretically. In practice, many games do not support multiple cores, or if they do, they often only support two or four at most. I don't have much faith in Paradox doing well with performance in this regard (I mean, it will probably be fine on release, when they push out a hollow shell of a game with next to nothing inside, but after a couple years of content bloat, who knows?). Speaking in general, it is better to seek a balance between the number of cores and individual core performance