Stating a fact without an argument, in somebody else's custom modded Oblivion, saying a 2-4 fps increase with HrmnsOblivionScriptOptimizationv1.0 enabled using TDT and an external program it's a placebo effect, EVEN when the fps are gone with the esp disabled (and due the already low frame rate this PC handles, 2-4fps makes a visual difference) has to be a very wise observation... or not.
Show me a statistical anolysis of your FPS with and without the mod, and I'll consider what you have to say. Until such a time as you produce such an anolysis, everything I know about Oblivion, it's scripting engine, and what affects its performance, as well as my own tests with the mod, tell me that you are absolutely wrong, and in fact the effect you describe is impossible.
Oblivion's real CPU eaters are AI heavy mods. The AI system will bring you down far quicker than any script unless that script is badly written. None of the vanilla scripts are badly written.
This. There is no script written for Oblivion that is a tenth as complicated as a single NPC's AI, barring actual bugs. I'd be surprised if there are any even a hundredth as complicated. While I'd argue that some of Bethesda's scripts are "badly written" in a number of cases (a particular script in SI's chapel thing springs to mind immediately), none of them have such a glaring, performance-destroying bug.
If you are having performance issues, the first thing to check is graphics settings, graphics mods, and your computer's graphics capabilities. If you've assured yourself that everything in that area is running efficiently, you might consider AI; large crowds of NPCs will cause problems for even the greatest of CPUs. Since Bethesda did a reasonably good job limiting the number of NPCs in one spot, and most mod authors try to as well,
for most people the graphical processes are the major bottleneck, and improving CPU issues does nothing so long as its waiting on the graphics card to finish everything - which is the situation that most Oblivion installs find themselves in. Only if you're in the highly unusual position of having a stellar graphics card and a terrible CPU would I even worry much about AI (barring a mod that adds ridiculous levels of crowding), since graphics are almost certainly the culprit. Scripts don't even come into play.
Note that this is very different from
Morrowind. In
Morrowind, Scripts could absolutely cripple the game; they were not nearly as efficient as
Oblivion's. Modders had to be a lot more cautious about their use and substantial gains could be found by optimizing them. While it is always best practice to optimize your script as much as you can (after all, no point in
wasting CPU time, that's just sloppy), bug-free scripts are basically never going to affect your game's performance.
(barring the brick wall effect, which is basically not going to come into play under any actual play scenario; you have to be
trying to hit that)