I can run from the High capacity feeder loading 250 at a time, and I did increase it to 65 per min. by tweaking a few settings.
First under service mode you can extend how long it runs in between gradation adjustments or whatever that printer calls it. I had a service tech in for that. This only made a minor speed improvement.
Second I redefined the standard env weight of 200 gsm to standard paper of 86 gsm and still didn't get seams showing and had good toner adhesion. While resetting the paper I turned it and ran the short direction the 6 instead of the 9. Now my speed for those are at 65pg per min. and I can load 500 in the big drawer.
SCORE -- my new favorite laser envelope machine yet.