I don't want a copy of GTAIV (already have a legit copy) but iCEnhancer 2.1 claims that 'Framerate +25%' on the page,http://www.icelaglace.com/
Maybe that was the mod Hexit was talking about.A few points-
1)Try running contig.exe.It's a microsoft tool.You can google it.It apparently increases fps.
2)Keep it at 188.8.131.52,patch 6 did something to the way shadows are rendered.
I am not sure,you would have to read the changes list of the patches though.You can read them here-http://games.softpedia.com/progChangelog/Grand-Theft-Auto-IV-Patch-Changelog-30489.html
You could try installing the game without any patches,make a backup,try 184.108.40.206 and 220.127.116.11 separately and decide which patch to keep for yourself.:)
3)This mod here http://www.gta4-mods.com/tools/ivpm---gta-iv-performance-manager-get-more-fp-f14136
claims to give more fps but the author later claims that it is for those players who are unable to play due to lag.
4)A miscellaneous mod I found which actually works as per the comments-http://www.gta4-mods.com/misc/more-fps-f18313
I did not try this mod.
You could try searching for tweaks but be very careful while trying them out.Some of them can render your game unplayable or worse,buggy.
Hope this helps.:)