SlewRate and Output Swing for a differential OpAmp
SR rate is correct. Take a look on https://payhip.com/b/5Srt ("ch.  1.4.  Slew-rate" in a paid version. I have that position at hand, so I'm using the info from it.):







or any other position like Razavi or Baker (http://www.designers-guide.org/Books/).

What you need for fully differential opamp is the feedback. If you will use your opamp like in your 2nd picture (when you define names for inputs and outputs), you have a comparator. SR is still possible to be calculated (you need take into account the offset and set outputs to the desired level, e.g. VDD/2), but with the feedback it is easier and this is how you are using your opamp so you can get real results. Once you have feedback, you just apply input voltages to vi1 and vi2 in the opposite directions (e.g. pulse voltages as in the picture you provided or Fig. 1.21 above) and calculate slew-rate on raising and falling edges.

For the output swing, THD parameter may be used. It is described in "ch. 1.1.2.  Output voltage range" in a paid version of https://payhip.com/b/5Srt, but you should be able to find it somewhere else like here:


https://ecedmans.files.wordpress.com/2014/03/the-operational-amplifier.pdf
http://people.seas.harvard.edu/~jones/es154/pdf/op_amp.pdf


But still, you should have a feedback path. You just apply input sinusoidal signals and measure THD on your outputs.