GTX 970 core performance cap

Alright,

So I've been OC'ing my 970 for my Alienware 17 R2 laptop (desktop graphics amplifier), and have been pretty impressed with the ability this card has to push. Especially considering its the reference card (titan cooler) and is the only thing producing heat inside the shoebox. . . Nevertheless, I believe I have reached a point where my core increase no longer effects my overall graphics output. Curious what others may find as the reason?

I wrote a v-bios custom for it, that caps my voltage at 1.245v, and sets my BASE core at 1385and my BASE memory at 2000 (permanent overclock). I increased my power limits to 135% and wrote a custom fan profile to save to bios as well.

In Nvidia Inspector, I am able to set my power limit at 135% and add +215 to my core to make my core run around 1600 MHz (stable reading at 1597 MHz in GPU-z, max boost was just over 1700). I ran benchmarks pre and post, and gamed with my latest bios setting (previous I set my core to be maxed at 1503 and it held the core here). Running witcher 3 for an hour an my frame rate did not go beyond what it normally does, checking my log, my GPU was clocking around 1600 the entire time. In benchmarking, it peaked just under 1700, yet the score was unaffected by this?

So this was all to say - is there a point in which core performance clock increases does nothing for real life visible data? IS the max performance gain around 1500 MHz so there's no need to push the card any higher? Or is it just a limitation of the graphics amplifier? (my least suspected reason).

 

Making an assumption here, but in theory could it be a bottleneck from thet CUDA core or Shaders that stops performance increases? Meaning, the 970 is literally running at its max ability around 1500-1520mhz?