How is this possible? Valley bench scores

[ERIC J]

I decided to OC my evga gtx780ti superclocked even further just to see what % of performance i would get
and took a few unigine valley bench marks.
what i seen has me confused? at its factory setting i scored 3117 and with a OC of 150MHz more on the core clock and 350MHZ on the memory i only got 3074?
The card is running stable but got a lower score and the FPS was not really improved?
I am new to overclocking and am having a hard time understanding a lot of this

 

[Yamitime]

It means don't overclock ,Your card was going past its thermal range and started to throttle back to control the extra heat . Hey at least come winter you wont need the heating on :0

 

[damric]

Probably unstable VRAM. It can be unstable without crashing and just cause a bunch of errors and lower performance.

 

[ERIC J]

Probably unstable VRAM. It can be unstable without crashing and just cause a bunch of errors and lower performance.

it is a 3g card but i thought when using valley 3G's was enough?
other with the same card have scored higher on valley?
My temps never went above 71 degrees during the test

 

[ERIC J]

It means don't overclock ,Your card was going past its thermal range and started to throttle back to control the extra heat . Hey at least come winter you wont need the heating on :0

I was told this card is safe all the way up to 90 degree's and my 780ti never went above 71 in the tests?