Steel_Nugget :
I have a I5 2500k @ 4.3 and in BF4 my R9 290x and GTX 780 can't reach 100% all the time, while my CPU is at 100% usage. So yes the I5 2500k will bottleneck a GTX 780 in some games. Sadly I was misinformed when upgrading as well.
R9 290X and GTX 780? Which is it?
What frame rate is this at? If higher than the refresh rate of the monitor there is no performance limitation at all from the CPU.
I also find it very hard to believe the CPU even hit 100% for any length of time.