GTA IV on PC - Cannot run well on high texture detail  

Hi, when running GTA IV on high texture detail, most of the background textures do not load in straight away (or some appear very blurry) and may take up to 30 seconds to be shown. Textures include buildings, posts and roads as shown in the screenshots below:

http://homepage.ntlworld....
http://homepage.ntlworld....

After doing some commandline.txt tweaks as shown here:

-fullscreen
–novblank
-norestrictions
-nomemrestrict

The game runs really smooth (35-50fps) with details on high (over 60 draw distance etc) and textures appear much faster than without the tweak, but objects and textures now pop up at you out of no where and many of the textures still take a while to load.

When adding "-availablevidmem 1.95" (anything over 2.0 crashes my game when Niko leaves his appartment room) to the commandline.txt file, the textures load in fast and good but the frame rates are not smooth. Often it would go from 25 to 15fps and major stuttering appears. Lowering things like draw distance and draw detail from say 60 to 25 does not improve the fps much at all, with only 1 or 2fps difference. However the game still stutters often...

When I turn textures to medium, the game runs extremely well at very high draw distances and hardly any stutter but of course, the textures look blurry now.
I have read many threads on this forum and I am not sure what I can do. Any ideas?

My specs are:

Intel Core 2 Quad 9450 (With Thermalright Ultima Heatsink & 120mm Fan) - 2x2GB Corsair XMS2 DDR2 (PC2-6400) 4-4-4-12 - eVGA GeForce 8800GTS 512MB - Abit IP35 Pro XE - Hitachi Deskstar 7K1000 750GB - Corsair HX Series 620W - Creative Sound Blaster X-fi XtremeMusic - Hyundai W240D-PVA 24" - Hauppauge WinTV HVR-4000 - Windows Vista Home Premium x64 SP1
I am using driver version 180.84