well as you see its a hit or miss or you have to find the trick to make that card work most times it when you go to a higher end card than what hp allows could be a unsupported bios for that card restricted slot power and so on
hp is in business to sell computers not have you upgrade as you want if yopu need a better computer they got a model to sell.
each model has its fix in some way and you got to rely on hp for all support as they want - this is why we do custom builds and leave the walmart computers at walmart
about all is see like at hp forums or where ever you can on your model and see what you can out side of that its all your own risk as I say you buy -- you try-- and hope you don't cry
good luck
that model of yours at hp came with a 6850 ?? I still use that card with out issues ..
also you see here it gives cpu upgrade info and memory but not any for gpu .. whys that??? so just do as you fell is best and keep them fingers crossed
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c03014584&cc=us&dlc=en&lc=en#N290
also you see how out dated your support is ?? so if that card needs a bios update to work if it did not on your try your just s.o.l
http://h10025.www1.hp.com/ewfrf/wc/softwareCategory?os=4063&lc=en&cc=us&dlc=en&sw_lang=&product=5156849#N3681