Depends on what games you play...

my friend has a hd 7870 (equivalent to R9 270X) plays War Thunder and Valve games smoothly and is happy with Catalyst 15.3 from Ubuntu repositories, though catalyst 15.9 would be better.

If you play a lot of Wine games or COH2, i suggest you try Radeonsi, since it gives much better performance through Gallium Nine, but according to https://www.youtube.com/watch?v=HF2VXEoTKBc it is a bit of trial and error, so Catalyst IMHO is more reliable.

I would not recommend an AMD graphics card at this point since a lot of games on Linux don't support AMD, or the performance is not up to par. Stick with Nvidia until AMD gets their act together.

If you want to support AMD buy an APU based (mobile) system for secondary light gaming or as a steam streaming client. As it stands right now, no point in getting a dedicated GPU from them for Linux gaming.

Well, I've been quite happy with this 370 and the open source drivers. It's definitely not a performance beast (except in Wine) but overall I'm am not too disappointed.

which games you are playing ?
My main focus is dota 2 maybe borderlands and magicka 2 when it make linux debute.

Mainly Verdun, some CSGO with Liam, Mount & Blade: Warband, I've tried SOMA (runs fine) and plenty of Freespace 2. Your biggest problems with a card like this are going to be those big games and Borderlands 2 for example might not run as well as you'd hope. The Pre-Sequel runs amazingly well though. As for Dota 2, you'll get excellent framerates out of it even on the open source drivers, the Rebirth update made it quite fantastic.

Thanks.
What framerate can expect on dota with max settings in open source driver as last question :)

70 to 120 FPS at 1080p with everything pretty much maxed out if I recall correctly. It was constantly at or over 60 FPS.