Have you noticed where they're actually running on electric? Primarily in the tunnels approaching Grand Central Terminal and Penn Station in NYC. High speed is not needed or allowed in those areas. Once clear of the tunnels, they switch to diesel where full power is available. In any case, 3rd rail extends only to Harmon on the Hudson line and Pelham on the New Haven (NEC) line. [en.wikipedia.org] While I couldn't find data on specific top speed for the P32s on electric, it's probably similar to the LIRR DM30s: 100 (110 for Amtrak) on diesel, and 80 on electric, which operate under similar conditions. Lack of data in this case makes no difference: the use case on electric power does not call for high speed.