GPU core OC vs. VRAM OC

[Dunkan77]

Hello,
I am fond of OC and I do it whenever I can. I can't help but notice that on graphics cards, you can OC the core by 100-200 Mhz or more especially on the GTX 970 but the VRAM OC is phenomenal! You can increase it's speed by 500 Mhz or more on many GPU's (not effective clock speed). Why is that so? and why does the GPU core OC on its own gives your a lot more fps than a VRAM OC on its own? Of course, you will get the best results by combining the two.
Thank you for answering with concrete facts and arguments because I really want to know why: the curiosity is killing me 😛

 

[Zerk2012]

http://www.hardocp.com/article/2011/08/17/asus_rog_matrix_gtx580_platinum_video_card_review/11#.VKaop40U_yc
A video card can be thought of just like your motherboard, processor, and memory. You will get better performance from overclocking the processor than the memory.

 

[Icaraeus]

The reason you may be able to overclock VRAM more is possibly because Nvidia didn't make it very high to fit TDP requirements. Raising core clock will always provide more of a boost as you're raising the actual speed of the graphics chip - memory speed doesn't make too much of a difference, but it does make a difference.

 

[Xyos]

The clockspeed overclock affects how fast the GPU can operate, the faster it can operate the more it can render at once. Memory overclocking does not really yield any tangible overclocking results. Textures and other assets like render frame information (made larger if using anti-aliasing or super-sampling) are moved to memory. Access speed in relation to memory operating frequency does not really have any speed benefits. Having more memory available is much more beneficial (run games at higher resolutions+anti-aliasing+better textures).