What is the appropriate horsepower (wattage) for a new pair of PSB T2's?

Interesting question. Why do you think it matters?

I have T3's. The 3's leveled up considerably when I upgraded from a NAD M27 to a BAT VK 6200. Sound overall became much richer and more detailed in the bass. I listen to 2 channel and watch movies in a 5.1 system with 4 T3's and a center C3.

The T's need good current delivery more than anything. Get something that doubles down to at least 4 ohms. Watts?  I'm not sure. My BAT does 200 per channel. 

The main factors in deciding what power you need are the size of your room, type of music and your preferred listening level. Those speakers are fairly sensitive (90dB) so unless you have a particularly large room then you probably don't need anything greater than 50W and can probably get away with a fair bit less.
If you have a digital multimeter and a digital source (DAC etc) then there's an experiment you can do to work out how much power you need at your preferred listening levels. If you're interested I can find a link to the instructions.

Regardless of wattage needs, there are definitely some speakers that benefit from amps with higher current output and/or higher damping factor.  I've heard this with two amps demo'd on the same speakers.