wondering if a i5 4460 and a gtx 750ti paired will have a bottleneck and if there will really be much of a performance boost upgrading from an i3 4160 CPU
I doubt you will see much boost as you will be held back by your GPU. Your current setup is a good combo, to get a boost you really need to upgrade both
It will be a bit better in CPU heavy games but other than that you won't notice a big difference until you upgrade to a better graphics card. Something like a GTX 960, GTX 970 or R9 280(X)/R9 290(X).
I doubt you will see much boost as you will be held back by your GPU. Your current setup is a good combo, to get a boost you really need to upgrade both