Hmm Hmm Hmm...
FPS problems with ESF have a pretty good explainable reason...
The half life engine, which is based off of quake 2, has a very small polygon count that can be rendered withing reasonable frame rates compared to other games. Other mods to half life, ns/cs/tfc, all have small indoor areas followed by small outdoor areas. The engine only has to render small portions of it at a time, resulting in higher fps and lower polygon count. ESF, on the other hand, is an all-open map, and the engine has to render every single polygon on the map constantly. This is where your fps is shown. It is rendering everything and everyone on that map 18 times a second, for you. This is a load of polygons, for the half-life engine, and results in extremely low fps compared to other games and/or mods.
Just lower your settings, overclock your graphics card, get a better cpu, or just try every config tweak available.