im getting a gigabte 670 in the end but is it a good overclocker?
You can't guarantee any overclock unless you buy a card specifically built for it (such as Lightning's and Matrix cards).
Buy the best card you can afford to buy and then when you have it you can hope it overclocks well. But if you buy a stock card hoping it will overclock and it doesn't, well, thats the gamble you take.
I had two stock PCB 7970's and one reached 1300core while the other topped out at about 1150 (and had a much restricted BIOS).
Reference boards are very much luck of the draw and if you buy a card that doesn't overclock well then it can be hard to send it back.