If you use the EZ-supplied boost elbow, the EZ will inhibit overboost codes when you plug the EZ in series with the MAP sensor connector - it has a boost module built in.
We installed the EZ (with boost elbow) and Jardine 4" exhaust the same weekend, so I don't know how much each contributed, but the results were as follows when towing our 13,500 GVWR 5ver:
Stock:
Max pre-turbo EGT: 1250-1300 degF
Max boost: 22 PSIG
With EZ & Jardine 4" exhaust:
Max pre-turbo EGT: 1050-1100 degF
Max boost: 32 PSIG
Rusty