I haven’t done it yet. I went the other way and removed that giant box muffler under the truck and replaced it with a Stainless Works straight-thru first.
Based on that, my truck is louder outside, but is still drone-free, and if you have the radio on at all you can’t hear the exhaust note. Still seems quieter than my wife’s Platinum with that ridiculous artificial engine noise being pumped in. I’m rather deaf, so I don’t entirely trust my auditory senses.
Not sure about performance gains, it’s difficult to tell with the EB.
I’d guess you wouldn’t even notice it’s gone as quiet as the Expedition is inside.
I’d probably kick it out the side rather than straight back if I ever remove mine. But Magnaflow says they are developing an exhaust for the EL finally, so I’ll probably go that route once it’s released.