1. You can take this argument right back to the days of dual core vs single core CPUs.
2. Has multithreading increased lately? Probably not as fast as we have hoped, but yes and apps will continue to be better at using mutiple cores.
3. Do these processors OC to similar clocks? yes, even my 1055T gets all up in the 4.0Ghz range on a 890gx board, with little to no skill on my part.
4. Do you feel bad about having a 25% increase in TPD? The x6 have better idle core clock control features as well as Turbo core. If you rarely reach full load, then that max TPD is irrelevant.
5. Think of the resale value of a x6 in comparison to a x4 3-4 years from now. How much do Q9550 now go for compared to the e8400 for example, almost as much as what they cost new. This happens because if you are looking to replace a toasted CPU, you will most likely look for an upgrade as well, and the x6 is the fastest cpu you can get for an AM2+ mobo.
Hope these examples help.