hi there. im running similar stats to you. intel core i7 2600k 16gb ram and im running windows professional (x64). with 8gb of ram you can run the 64 bit system. believe it or not the 64 bit system is cheaper than the 32! (only a little) but it is go for professional or ultimate. but bear in mind ultimate is £30 more.
any of them which are 64bit will do you fine really. unless you want the additional security of ultimate (bitlocker etc) then there is really no need to pay extra for it. so anything from home premium upwards will be fine for your uses