Mine was deleted for a few years and it would take forever to get warm in winter. Last year I put the emissions back on and this winter it's blowing warm air after driving only 5 minutes. I credit it to several things including increased back pressure from the filters and increased turbo vane position (50% now while driving, 29% when deleted). But I believe the biggest contributing factor is the EGR. The hot exhaust gas getting pumped straight back into the intake would definitely heat the engine faster.
BTW, fuel economy only dropped about .5 MPG with emissions back on.