The biggest issue that never seems to be touched on; the DK2 is a huuuuuuge improvement in terms of overall pixels over the DK1. 1080p x 2, so really, it comes down to optimization and planning. Smart use of culling, simple materials, and not running the game in the editor will be huge. You can right click on your project file, and you should gain 30-40fps (I did).
That being said, a lot of people are using the rift with underpowered GPU’s - I believe that Lucky Palmer stated that currently the GTX 770 is about as low as he’d go while developing for the rift. Also - stay away from bright lights, as they will cause massive screen jitter - neutral scenes without a stupid amount of contrast between light and dark areas will work infinitely better.
You should be able to use the HMD SP command, press alt + enter to get out of full screen, and then press alt+enter again to re-enter full screen with a lower screen space resolution.