The following mechs are all limited by netcode to the same top speed regardless of their theoretical max engine rating:
Jenner
Cicada*
Spider
... and anything else that could theoretically go faster than 149 or whatever the netcode speed wall works out to be.
* - I think these have variants where their top speed is limited by engine size before netcode speed wall kicks in.
Edit: Updated the above list with corrections as quoted below:
Sandslice, on 15 January 2013 - 01:03 PM, said:
Crossed out the two 50 tonners. IIRC their stock 6/9 speed puts them under the threshold that Sandslice describes.
Edited by Bagheera, 15 January 2013 - 01:15 PM.