Will my aging PC be able to handle GTA 5 on decent settings?

"aging". Ha. Your 2600k is just as good as the latest i7's. Marginal gains have been made from Sandy Bridge to Haswell, and your 4.5Ghz would easily close the gap. The 760 is still a decent card.

Go to youtube and search i5 or i7 (make sure its 2nd to 4th gen) GTX 760 GTA V and see the settings people are playing with in their gameplay videos.

ex:

[video="https://www.youtube.com/watch?feature=player_detailpage&v=MQ7L9-a85kw"][/video]
 
Aging? LOL! I have GTA V installed on my 6 year old Core2Duo E7400 machine (yes, that's below minimum) but I did install an R7 260x 2GB video card (on a PCIe 2.0 slot) because the game stuttered horribly with my old Radeon HD 4830. Game runs like a champ with the new video card.