Which mods will best improve FPS on low end machines?

I have streamline, anything else I could use?

The obvious Oblivion Stutter Remover, coupled with newer mods/ tools such as Oblivion Reloaded (framerate manager), ENBoost.

Id ditch streamline for Sztermels recommendations

As an alternative to one of the major "FPS killer" mods - Better Cities, you could try some of the mods created by http://www.nexusmods.com/oblivion/users/5214851/?tb=mods&pUp=1. They're all separate mods each altering different parts of the IC and BC is modular...so I guess you could make your own combo. Plus what others have already suggested....OR, ENBoost. Use windowed mode in OR.

A bit off topic

The largest increase in FPS I got, over 15...in some locations over 25, was after I disabled Vsync. In my case it wasn't good because I got screen tearing after that and it's ugly, so I've turned it back on.... Screen tearing doesn't happen on all configs...so you might want to try and disable it, see if it helps.

Use DDSopt to compress textures. You have http://wiki.step-project.com/Guide:DDSopt that folks at STEP forums made, it explains every single detail about this utility. DDSopt is extremely helpful!

Now assuming you're on Windows 7/8 you could try the following... Assign one CPU core to Oblivion.exe. Leave the first core to the OS. You have several utilities for that, i used Process Hacker. If you're on Windows 7/8 and your CPU is one of the Intels i3,5,7 there's a small OS tweak which will keep your CPU cores always awake. It's called unparking the CPU cores and to help you with this there's a small utility called http://www.coderbag.com/programming-c/disable-cpu-core-parking-utility. I used it without any problems whatsoever. http://www.thewindowsclub.com/processor-power-management-windows. It doesn't matter if it's Desktop, still applies. Before you start playing the game, shut down all unnecessary processes and turn off your network adapter. That will help your CPU and RAM a bit...not much, but every byte and cycle counts. I got 2-5 increase in FPS, depending on the location - and no, it's not a placebo..

Speaking of shutting down background processes, I found that shutting down antivirus helps a bunch. When I used to have McAfee, shutting that down gave me a 15-20 FPS boost. Now that I use something more lightweight the increase is less, but still noticable. Of course if you are going to do that, it may be advisable to disconnect from the Internet first and remember to turn antivirus on before reconnecting. My PC has no wireless connection and I disable the Internet connection before playing.

@GazdaPaja, aren't cores getting unparked automatically when the system detects running a game (that is Oblivion) to reach top performance in that task?

I never tried unparking only because I thought it's automatic feature of the system to do that.

I can also suggest CleanMem as it's advised for Skyrim, but can be used for any game. Don't know if it actually can help much but talking about heavily modded Oblivion one should consider every available option imo.

Yes they are, but the point is - you want one core dedicated JUST for your game and you want it fully utilized. Another problem is that your OS expects ALL cores to be available so it can switch running processes between them. That's why you want them all unparked. If you're running a default Windows 7 you have bunch of unnecessary services all of them running in the background, plus who knows how many 3rd party software tasks, executing dynamically under it's host process called svchost.exe, thus eating up your CPU cycles. Depending on the OS's need they switch between cores. We all know Oblivion is unpredictable so who knows what happens in different situations while you play - how heavy is the CPU load while you're in a combat compared to the CPU load when you're just standing in the middle of a nowhere doing nothing....I guess there's a difference, never tried to benchmark it but considering the sound of my cooler in those situations I'd say there is a big difference. And while the game is not so resource intensive, OS can switch it to some other core because some other process, or more of them at the same time, is asking for more CPU resources, say - scheduled Windows Update, Prefetch/Superfetch, AV scan/update (depending on the vendor some of them to this whether you play a game or not)...etc. Those few tasks plus the game will each access CPU cache so that the CPU can reduce the time needed for them to access RAM. When you set the CPU affinity to a specific core for the Oblivion.exe process you're allowing that process to better utilize CPU cache and the assigned core for itself, resulting (theoretically) in a more fluent and stable gameplay (less stutter, higher FPS...etc). For me it resulted in a slightly higher FPS increase. When you run a dependency scanner on the Oblivion.exe you'll see that it depends on the dsound.dll file which in return depends on the powerprof.dll file. Powerprof.dll file is a Windows component and is used by the Windows power management system, the system that is affected when you change the settings inside the Processor Power Management (minimum and maximum processor state percentage values)... Does changing those values to 100% affect anything? That setting alone...I wouldn't say it does, but combined with some other small adjustments (call it tweaks or whatever) I'd say it does make a system snappier and game more stable, at least in my case...

edit: Ethetan sorry for hijacking your thread man...this was completely off topic