OC'ing is dependent per card. You can have two identical cards. One may overclock and the other may not. I had two identical 8800GTS 512 cards back in the day (same make, model and BIOS). I couldn't overclock one at all and the other would overclock very well.
Usually most people look for the mini cards to run in mATX case builds. You shouldn't experience any real difference between the cards, other then maybe how well one may cool over the other.