When i looked some years ago they were silly money compared to E85.
I bought some cheap E85's to see if i could modify.
Never got around to trying to replace.
I think the plan was to Dremel a section off so as not to remove the axle.
I'm happy with the B4 on my 23i on country lanes.
I ditched the B6 that look better quality for the extra cost.
But you don't see them on a daily basis.
Ride is not vastly softer.
Disconnect the maf sensor i think it runs in a sort of basic mode.
See if it runs smoother.
Few things i had with car was cam cover was bowed and oil in spark plug hole 4.
Also had faulty ambient temp. sensor fail behind left wheel arch liner.