> The P32AC-DMs (Amtrak & Metro North) can do 110 on diesel, not electric.

Speed isn't dependent on the source of the electricity which spins the traction motors, although it is dependent on the amount available. In diesel mode, the amount is finite (3,200 HP, max with no HEP), while in electric mode, this limitation isn't quite so stringent. After all, the NYC ran the ex-CUT electrics on the 3rd rail, and they drew a lot more current than a P32 could ever hope to. GE designed the P-32AC-DM for a maximum speed of 110, which as I said before is printed in black and white in the operating manual (without reference to where the electricity comes from).

> 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 the real world, operational considerations also come into play which apply to all locomotives, steam, diesel, electric, and dual mode: 1) territorial track speed (curves, etc), and with electric operation 2) considerations revolving around current collector limitations (which aren't unique to over- or under- running third rails).

There are reliable industry-based reports of the S-motors operating with trains at speeds of 65 MPH (GE's speed/current curve for the S-motors maxes out at 95 mph). A number of the T-motors, particularly the passenger ones, had similar "top speeds".

A P-32AC-DM can do high speeds on 3rd rail, provided it is allowed to do so.