I know it specifically states that the user is only interested in single-threaded apps, but I would still recommend the i5-750.
In single threaded apps, the i5-750 is going to Turbo Boost itself up to 3.2 GHz, so it's not like it's slow. It is also very overclockable and has great efficiency with moderately high overclocks.
I just think the industry as a whole is moving towards more and more cores. If you have the budget for it, why not buy the four cores. Six-core processors are here, and soon to be eight-core for the consumer. I just don't see much sense in getting a dual core UNLESS you are trying to save money. But if you are trying to save money, I would just get the Phenom II X4 955. You still get the four cores, and save fifty bucks.
Maybe the op should consider what exactly he needs a "fast processor" for. I mean if you aren't doing gaming or 3d work or multithreaded applications, then why DO you need a fast processor? What single-threaded applications are you running that require a really fast processor?
If all you are doing is email/internet/office apps, you could easily get away with spending $100 on a really fast dual core.
I guess I'm a little confused here on what the op needs but those are my thoughts anyways.