If all you do is play games then an i7 is not necessary. The vast majority of games do not make use of Hyper Threading (HT). If you use programs like video editors that can make use of HT, then it would be worth having an i7 because HT can improve video encoding performance.
8GB of RAM will be enough for most people including gamers. There maybe a handful of games that recommends more than 8GB of RAM, but I don't know them off hand. If you have a lot of programs open or work with very large files, then having 16GB of RAM or more can be beneficial.