What are the strong improvements?
I've only seen a slight improvement of 4% in Unigine
edit: Can't do a comparison for Metro 2033, but for anybody elses reference.
with i7 950 @ 3.9 ghz / 570 @ 890 hz and
Settings: 2560 x 1440; DirectX 11; High; AAA; AF 16X; PhysX: Enabled; Tesselation: Enabled; DOF: Disabled
Averaged 40 FPS on 3 benchs
The average FPS drops to 28 on Very High
Then your pc is crap and faulty.