Please post your system information as requested at https://github.com/ValveSoftware/steam-for-linux#reporting-issues.
Some discussion was had over at http://steamcommunity.com/app/221410/discussions/0/846938351169300407/ on the topic of using -dxlevel to essentially improve performance in a pre-translation way. Not sure if it actually worked, but I experienced smoother gameplay and higher FPS but a TF2 update came out around the same time. Might be worth a try.
EDIT: I just threw < -dxlevel 60 > at HL1 and got ~60 FPS on my netbook (1.6 Ghz processor, 1 GB DDR3). Everything was kinda matte, but it played very....very... smooth.
Closing loose ends. Fixed.
Nothing extracted yet.
Found that looking from one side of maps to the other causes huge performance drops, could this be that the engine is trying to render too much and something is missing to tell the engine that it doesn't need to render everything where the player is looking.
EDIT: Forgot to add