To add on to what Noah said ..( didnt edit ..in due respect to what Noah said )
You could try launch options like
-novid
or even try toggling GlSl on mac..
Further more you could lower your screen resoultion when you play...remember the higher resolution the slower it gets..
use options like -h x -w x where x is the variable and h and w is height and width respectively (sorry was doing Additional maths before writing this post)
use launch options like -sw for windowed mode
Well..Wine and Crossover arent really perfect science ..but they are good effort.
Give them your time and patience and we , together , might just make your games work :)
yea...so feel free to post your L4d problems and rants 😀