Indy LA-X vs. Eddy heads

Coatings help to minimize/neutralize the difference between iron and aluminum, performance-wise.
If your engine is overheating in traffic then it just isn't right. The fact that your engine overheats means that either your engine is not properly tuned or your cooling system isn't up to the task or both. This should be fixed, not used to sway you towards iron or aluminum heads.