Low GTA IV Frames

Hi. I know there are a lot of threads about having low frames in GTA IV. But none really have the same specs as me so I thought I would just make a thread and hope I'm not going to annoy someone with yet another low frames GTA IV thread.

Anyway, as the title says I'm getting pretty low frames in GTA IV.
My specs are as follows:

Intel Core 2 Duo E7500 @ 2.93ghz
4gb OCZ Gold Edition 1066MHz RAM
1TB WD Caviar Greenpower HDD
Asus P5Q-SE2 Motherboard
Vantec Ion2 620w PSU
Asus Nvidia Geforce GTX 260

Here are the benchmark results:

Statistics
Average FPS: 49.18
Duration: 37.01 sec
CPU Usage: 79%
System memory usage: 52%
Video memory usage: 45%

Graphics Settings
Video Mode: 1440 x 900 (75 Hz)
Texture Quality: Low
Render Quality: Low
View Distance: 1
Detail Distance: 1

Ok, so I have everything on lowest and the benchmark test tells me I have good frames, but in game I'm only getting an average of about 33fps, sometimes around 25fps and even down to 16fps.
I know that GTA IV is optimized for a quad core CPU and that it's requirements really badly optimized and such, but really, shouldn't I be getting higher frames than what I'm getting, especially as I have everything on lowest?

Anyone know whats happening or is this a normal sort of occurrence?

P.S Sorry for the long post =P

EDIT: I have tried on settings higher than lowest but most of the time it's almost un-playable.

OK then, that sucks. GTA IV is fun anyway.
Yeah, was just playing Crisis Warhead on max with 16xAA at about 30fps.
To bad then for GTA IV, I have read quite a few times that GTA IV is broken I just expected slightly better performance on my PC.

Thanks anyway for the reply.

Valve, Blizzard, Polyphony and Codemasters with a few others are the only ones left - who test intensively before releasing new titles imo.
GTA 4 is such a bad port, the only way to get a good average framerate is to go triple- or quadcore.

My average fps in GTA 4 is 49. My computer specs are:
Core2Duo E6750 2,66 running 3,5Ghz
8Gb Kingston HyperX Running 1:1 @ 4,4,4,12
Geforce GTX260 V2
Soundblaster X-fi Xtreme gaming

Batman Arkham Asylum: 8QCSAA, 1900*1080, every setting on highest and High Physx setting runs with a 58fps average on this machine and looks 10 times better than GTA4.

Cudos to developers making good game-engines.