Brand matters, explaining...
Nvidia/AMD sell basic chips to manufacturer cards like EVGA, Asus, Powercolor, etc. and then, they start to build a graphic card based on that chip, they buy memory too from other brands, like samsung or kingston.
When assembling the whole card every piece count, and even using a good central chip, every other parts like capacitors, resistances and peripheral pieces can be from brands or materials not as good. That decides the longevity of the product as the overclock capacity, because even if the central chip is very stable, others could not be.
Bottom line, if a product is expensive, usualy that means the whole assemble is good.
Also be aware that even within a given brand, they make several models based on a given graphics chip (i.e. XFX offers several AMD 7850 based GPU's). And a few of them are great, but 1 or 2 of them are dogs. It's best to read reviews at places like Newegg.com for any particular make and model you're considering.
Thanks for the help guys, however i still need an answer to my question
If you were to choose, would you go for the more powerful 7850 (even though Powercolor isn't as good as EVGA in terms of reviews) or would you go for the EVGA 650 Ti (because EVGA is a more "reliable" brand) card?
to an extent, if you're looking for reliable build quality, good customer service, quality cooler performance, then choosing the right brand can matter. granted you'd still be able to get what you want with something lesser, but most people want some assurance on the stuff they buy.
as for your question; i'd risk grabbing that 7850, branding be damned. far better performance over the 650ti, for the right price. maybe don't OC the card if you're suspicious of it's build and cooler quality?