General buyers advice when purchasing a graphics card?

Without using anything software wise, what do I need to consider when i want to purchase a GPU, (I don't want to get an under/overpowered card.

Do i need to purchase a GPU at the same price as my CPU or the same GHZ (or something like that?)

I know there is no given "Formula" to do this, (but just some general buying adivce without using a situation / part list)

thanks in advance guys

Well what will you be using it for ?

Do you have a PSU/PC already or is this just an upgrade to an existing build ? 

Whats your Budget ?

customer service in case your card pops 3 months from now. the components used(is it known to have a god awful coil whine?). does it run cool under it's own hardware design without software intervention to ramp the card to 80-100%+ fan rpm at stock speeds. i'd start with those 3 options and then buy what you can afford.