I5 and I7 are very similar. The biggest difference between the two as far as us humans are concerned is that the I7 has hyperthreading, and the I5 does not. The good new is that almost no games use Hyperthreading, so we can order the I5-4790K and save about $100.
The 1155 socket has been gone for awhile now. Even the last CPU's for the current 1150 socket will be out starting to hit the market next month. Late this year, or very early next year, the Skylake desktop CPU's will be using a new 1151 socket, which will slowly bring about the end of the 1150 socket boards.