8AT Transmission Slip?

I mean sure but that's the wrong point to be looking at back pressure. That's the bit you typically want reduced in a turbo engine.
You have pre and post turbine pressures to consider and pre is the point you want to ballance your back pressure post is where you can more or less open it up. Header tube collector size and style ontop of turbine housing size are the factors you want to consider. All of these factors change when you look to change from an open collector to a twinn scroll assembly. It's far more complicated than a black/white statement.
Coming from the subaru world you learn alot about it as from the factory that is the least efficient set up in existence l.

 

All I'm saying is back pressure doesn't help. That's it. There's many variables that go into tuning an exhaust but backpressure doesn't help.

Its not a perfect 1 to 1 comparison but it shows clearly back pressure isn't helpful. It shows the importance of how both the size and length of the exhaust play into how and where the power is made.

That's a Motor Trend series and does a lot of really great tests. I'd recommend the series if you've never seen it.

 

this..

 

I think the real problem here is that R4T is charging 1800$ for that exhaust...

 

Throw the words "off road ..." in front of any product and know that you're going to pay 50% more for it. I buy motorcycle stuff. If you search for "motorcycle cold weather ..." you'll find a lot of $800-$1500 outfits. But if you search for "snow mobile gear" you'll find the functional equivalent outfit for $400-600. Merely adding Motocycle to the product name is like adding Off Road to a product name.