I would say go for the i5 3570K, its the new Ivy Bridge tech so supports all of the new features (USB 3.0, PCIe 3.0 etc) and should give you a good CPU for years, just remember that you will need a more expensive Z77 motherboard for one of these.
As far as I can see there is no 3570 model, just the 3570K so you might have to look at either the i5 3450 or i5 3550 which are available here -
Scan Computers but like you said you might as well go for the K just to future proof yourself in case you decide to overclock in the future as its only a few £££ more.