I have a few enhance graphics mods but my framerate in outdoor environments suffers because of this, is there any mods that improve outdoor performance?

Try turning down the View or Object Fade distances a bit, that can help without lessening the graphics.

Something to keep in mind, my game is clamped at 40 FPS as this hides the inevitable frame drops, so if your not chugging outdoors, then maybe this is OK. Dropping from 40 to 25 is not noticeable, dropping from 60 to 25 is a bit jarring.

Skyrim performance PLUS

Hialgoboost