iMac 27" toggle display problem and advise

Hello guys,

Im new member on this forum (was reading only before) so now after a while i decided to share with you my problem and if you can help / assist me with decision. My problem with connecting pc and imac is very well exposed here:

https://discussions.apple.com/thread/2246912?start=75&tstart=0

(my Name is there NikolaSR)

In short my iMac 27" is mid 2010 (so should work) but seems my Saphire Radeon 5850 is not damn supported even i connected with miniDP-DP cable, so after days of frustration i decided to buy other gfx card for pc , so my question is will this ASUS AMD Radeon HD 7870 (2gb , mini-display port 2x on the card) will work? (with direct mini to mini display port cable connected of course)

If someone can confirm me or advise me about this before i blow money in air, thank you a lot guys!!

 

Anyone please?