Pentium G2120 is pretty fast, but nowadays games need more CPU cores and threads to process gaming data. G2120 is good to pair with AMD HD 7700 series/7800 series or Nvidia GTX 650 series/ 660 series, but GTX 760 is equivalent with AMD HD 7870 and GTX 670, so as a high-end card it will be bottlenecked by the G2120 CPU because it's designed for high/max settings gaming. Probably G2120 + GTX 760 will do fine in older games in high settings but the CPU will gradually bottleneck the 760 in the future or coming games.
May I suggest, that if your budget is tight to get a i5, u could go for Athlon II 750K(This quad-core CPU still may bottleneck the 760 but will do better than dual-core G2120) or AMD FX-6300(using 970/990X/990FX chipset but...