To answer some questions:
1) The 2500K does not have hyperthreading.. true. A hyperthread uses residual cycles of the main core. That amounts to about 1/4 of a core, more or less.
Extra cores or hyperthreads are useful with multithreaded apps. But for games, which will use few cores, typically two or three, the extra threads are not very helpful. The extra cache on the 2600k is of unknown value in performance. If $100 is not that important to you, get the 2600K. As an early adopter, I got a 2600K. But, I have turned off hyperthreading, since I can see that I rarely use even the 4 full cores. Had I the option to do it again, I would have used a 2500K.
2) I find modular/semi modular non modular to be a non issue.
A semi modular psu will have fixed attachments for the power leads that are always used, like the 20 pin main lead, a 4/8 cpu lead, and perhaps a 6 pin pci-e connector. The others need not be attached if you don't use them.
On a non modular psu, you will probably be using most of the leads anyway. Unless you have a small form factor case, it will be no big deal to tuck those unused leads out of the way. Non modular advocates claim that modular leads lose power and may come loose. I doubt that is significant on a quality unit.
3) If I am not mistaken, a pci-e motherboard slot can deliver 75w or 6.25a to the grapnics card. If the card needs a single 6 pin connector, then that is another 75w or 6.25a. 8 pin connectors are more. So to size the psu increase for a second card, add 75w for the slot, and another 75w for a card that needs one 6 pin connector, or 150w for a card needing two. In this case, the second GTX560 will add 225w, so you would need a 675w psu. It is unlikely that the full limits of the slot and leads will be reached, but that is the conservative way to figure it.
4) Bronze/silver/gold is an efficiency rating. If you pay your own electricity bill, better efficiency is good. Perhaps more important is that you will generate less heat and have quieter operation with more efficient psu's. I used a gold rated Seasonic X750 in my small form factor case for just this reason. Even with a GTX580, the fan does not need to turn on.
5) I think graphics vendors suggest stronger psu's than are actually needed. In part to allow for poor quality psu's that do not deliver advertised power. A substandard psu can make it look like the graphics card is defective, and graphics card vendors don't want to deal with rma's for that reason. I have no problem using their overstated requirements. A slightly stronger than needed psu will operate more efficiently and quieter if it is not at max load.
6) For your needs, any of the 5 psu's you listed would be excellent.