What is the GPU frequency and voltage of your crashing cards?
"Poor" card is when factory overclocked chip occasionally crashes under constant heavy load.
Yep, and some factory overclocked cards may actually need to be underclocked to run properly.
On a side note, i found a small toggle switch on my MSI 750ti's the other day which switches bios's i believe between factory overclock and stock, haven't messed or looked into it but the switchs may be on other cards aswell
This is correct, but only twin frozr gaming series have that switch. Regular MSI single fan 750ti's v1 and v2 does not have it:
http://www.tweaktown.com/reviews/6148/msi-geforce-gtx-750-ti-2gb-twin-frozr-gaming-oc-video-card-review/index2.html