The N55 in the OG M2 also supposedly was stronger at low rpm's but the top end wasn't and you couldn't extract much more power. So seemed to me to be part of the turbo design. The S55 designed to keep more power up top and also had a lot more headroom as well with the trade off being some down low lag. The S58 seems to be the same as we hear about the lag from X3M owners as well as the large gap between 0-60 and 5-60.
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