To start off I have a few mods installed. They are ELS, LCPDFR, a few police cars, a 1977 Trans Am, a dune buggy, and Icenhancer. Before I installed Icenhancer, I was getting around 40 FPS on average (which caught me off guard for a 2008 game, with my setup) so, I thought I'd continue installing my mods. I installed Icenhancer, and I was still around the 35-40 FPS range, I figured that Icenhancer would drop my frames down to at least 30 fps, but it didn't. I hoped that my system could max this game and maintain 50-60+ FPS. If I reduce ANY of the settings, I still get 35-40 FPS. In an uncrowded area, such as a beach, I get around or above 60 FPS. The weird thing is, is that my CPU sits around 60-70% usage, and my gpu sits around 80-90% usage, meaning its not utilizing my system to the fullest, so I should be getting better framerates than 35-40. Please help.
CPU: Intel Core i5-4670K @ 3.4GHz
CPU Cooler: Cooler Master Hyper 212 EVO
Motherboard: ASRock Z87 Extreme3
Memory: GeIL EVO POTENZA 8GB (2 x 4GB) DDR3-1600 Memory
Storage: Western Digital Caviar Blue 1TB
Video Card: MSI GeForce GTX 770 2GB Video Card
Case: NZXT Phantom 530 (Black) ATX Full Tower Case
Power Supply: Antec High Current Gamer 620W 80+ Bronze Certified Semi-Modular
yeah, you're gonna have to put a lot of elbow grease on this one. it's no surprise the game is horribly optimized to the point that you're likely to see better performance on a sub-$600 dual-core Pentium + 650ti over a $2K+ LGA2011 i7 + 2x770's (for clarification, it has happened).
you may want to start with the command line/config file/etc. fixes in the link above. not all that aware of third-party mods/patches that improves performance, but i reckon there should be one. though most of these mods apparently requires a downgrade to patch 126.96.36.199 if you've updated to 188.8.131.52, if the latter patch doesn't work out for you.