Electrics have the advantage of having a huge potential amount of power off the cantenary, and use that power to reach their high speeds and overcome steeper grades. Diesel-electric on the other hand - is much more limited as to the power it has to accelerate and maintain top speed. Remember that a diesel-electric's tractive effort is in direct proportion to speed, so 150 mph will only have 1/2 the tractive effort that at 75, so you not only need double the horsepower, but also the additional horsepower for the higher speeds and resulting increased resistance. It's kind of the little dirty secret that commuter agencies keep insisting on more horsepower for HEP and faster acceleration, ignoring the extra fuel and resulting pollutants. (Recall when SP thought 2400, 1750 or 3600 hp was good enough for the Bay Area commutes? Wonder what the HP/T ratio was compared to all the 4000 hp commute engines being built now?)

The biggest drawback I see is very simple - would using diesel-electrics invalidate all the existing EIR's? The "impression" that everyone has is that electrics have zero pollution, ignoring building the distribution infrastructure, transmission losses and the environmental impact as to how you generate the electricity. Even solar panels create pollution being made, and don't work at night.