Will installing Cyanogenmod speed up my Galaxy S? I recently purchased a used Samsung Galaxy S Captivate. While it seems fine for my purposes, it would be nice if it were just a bit faster, in terms of loading different pages more quickly. From what I've seen, Cyanogenmod claims that it's faster than many stock roms, since it doesn't use the company's extra interface, which, in this case, would be TouchWiz. However, Cyanogenmod would also bring my operating system up to Android 4.4, and I'm not sure how much additional power that would take. I'm also open to using older versions of Cyanogenmod, if that's feasible.

Would it be better in terms of performance to keep my phone at the stock rom or to install Cyanogenmod?
In theory, your phone should perform considerably faster with CyanogenMod 11, because KitKat was designed with entry/mid-level phones in mind; requiring only 512 MB of RAM to run. (See this page about Project Svelte for more information.)

CyanogenMod also adds a whole slew of features like Heads Up Notifications and Privacy Guard on top of the AOSP code, so your phone will not only be fast but also be very useful.

Keep in mind, however, that CyanogenMod (along with others such as PA and OmniROM) are third-party ROMs, and therefore lack the various "enhancements" that the manufacturer has made in the stock ROM; so don't be surprised if you see that the camera doesn't perform as well, the battery drains faster than usual, etc.