FPS capped on Linux (AMD fglrx drivers)

[Kano]

Do you know the difference between double and triple buffering when vsync is enabled? Also fglrx is the biggest crap possible for source engine (all new valve games). Best: return the card.

[PizzaCat]

Recently I bought AMD R9 270X 4GB Graphics card after my old card died.

I checked various benchmarks for this card on Linux before buying, I know Nvidia has much better drivers (but most of my Linux use is development oriented)
I was expecting stable 60 FPS, on games like Dota 2, CS:GO, Civ 5, Kerbal Space Program or War Thunder.
But somehow I'm getting extremely unstable FPS limited around 30, few spikes will go up to 60..

Turning vsync on or off doesn't have any significant effect... I tried it on various distros, and different versions of drivers.

Currently I'm using Ubuntu 14.04 and latest Catalyst 14.12, but the issue remains.

Is anyone else facing the same issue?