>>527435061
Not necessarily. An older system of mine (Intel i5 3570k + Radeon HD6950) would suffer from unplayable stuttering despite all the anti-stutter fix mods available online for LE at the time. The ultimate fix for that was a barebones ENB. Removed the stutter, gave me 60fps (outside Markarth) and even added some much-needed colour into the game.

The performance tax depends a lot on the ENB settings, which you can also tweak yourself on the fly and see how it affects your performance.