GT 710 Overclocking
I have a DDR3 GT 710 2GB Passive Edition from ZOTAC. As you all might already know, it is not ideal for gaming. Hence, I intend on overclocking it to gain a couple of frames for GTA 5 (gives about 35 max, drops down to 11 occasionally). I have read many articles online about how it is a low end card, which means that it has pretty high overclocking headroom, but mine seems to hit the dead-end at just about 100 to the core clock and 250 to the memory clock, which give me no gains. Any reasons as to why this is the case and how to overcome it?
Low end cards do not have high overclocking headroom. Pretty much every GPU within a given series uses the same basic silicon, and then gets binned based on performance. Your card is a low end card because it performed so poorly in the binning tests. Cores were disabled, the clock was limited, etc. because of defects in the silicon. Trying to unlock those cores or push the clock speed will just lead to instability.
The only real option you have is to get a better GPU. If budget is a consideration, you might be able to find a used GTX 1080Ti or GTX 1650Ti or similar for relatively cheap. Even a GTX 970 would be a vast improvement. However, since you haven't said what the rest of your system is, it's impossible to tell if you would hit other bottlenecks, such as because of your CPU.