EGR and performance questions

Since EGR only operated at idle and cruise, it probably won't affect WOT power. BUT if your engine passes ANY oil at all down the intake valves expect massive carbon deposits on the valves (you'll get some from the PCV) . This is not so great for any aspect of performance.

This is even worse on a diesel. One of the reasons VW put the "cheat code" in their engine management software deactivating the EGR was to reduce the amount of intake manifold cleanings under warranty. The side effect is increased NOx emissions.