I currently have an e88 N54 for the last 2yrs.
I had an e90 N52 before it.
Both are phenomenal cars in their own respect but here's my $0.02
Originally I thought the N54 was too much power, specifically the incredible torque... but then the addiction kicked in and before i knew it, hunger for more power and a tune soon followed :-)
So since you have an N55 now, I would recommend the 135i. There is no replacement for TQ and I think you'll miss that aspect too much.
|move over... please|