Don't get that wrong, but that thing isn't meant to speed up things but to limit and even out some.
It limits the system load by remaining at the given value instead of going 100+ fps over water or less dense areas.
It evens out the sometimes huge fps differences when looking around, on the airport (with low fps then) and then away from it (with high fps).

That's the purpose of the thing, no speed gained, only stability in the simultaneous usage with some (famous) tweaks as they sometimes may overload the system in "too high" fps situations where your CPU "overruns" the GPU.
The famous tweaks remove or shorten the buffer between those two instances, so the fps limit prevents too high loads then which otherwise could lead to a CTD.

Running FSX in unlimed fps mode (speaking of that internal limiter) always includes the downside to end up in blurry textures here and there, more or less severely depending on the load on the actual system in use.