I can't entirely attest to the efficacy of this performance mod for Skyrim as framerate is about the one problem I haven't had while playing TES5 on my main PC, but it did seem perhaps a little smoother on my puny laptop. The creator reckons it can add a performance boost of around 40% in CPU-dependent scenarios; for instance, around 10 frames per second to chug hotspots such as the lovely waterfall-based city of Markarth. It's been achieved, apparently, by fixing an alleged tiny oversight on the part of Bethesda.
Claims unofficial path-maker Arisu, "It works mostly by rewriting some x87 FPU code and inlining a whole ton of useless getter functions along the critical paths because the developers at Bethesda, for some reason, compiled the game without using any of the optimization flags for release builds." Also, "They'd just have to add the string "/O2 /GL" to their Makefile". That easy, huh?
I'll have to take him at his word on that, but it's not exactly the first instance of Bethesda suffering an accusation that they didn't give Skyrim the PC TLC it needed. At least they've now patched it to support more than 2GB of RAM and high-quality sound.
If there is indeed something in this patch, perhaps Bethesda will be inspired to perform such tweakery officially, as with the 4GB update.
To install the unofficial patch, first you'll need to grab the Skyrim Script Extender (aka SKSE) from here and extract its contents into your main Skyrim directory. Then, grab the TESV Acceleration Layer from here and dump the DLL file within into [your Skyrim folder]/Data/SKSE/Plugins, creating the latter two directories if necessary. Then, launch the game by running skse_loader.exe from the Skyrim root folder. Let us know if it makes things any better, eh?