While the PS75 and 120 are very similar in appearance and operation, the 75 is about 10% smaller in frame and weight than the higher HP Powerstar line. All the rest share the same frame, hydraulics, etc. The 75 does have the same basic engine though... the time tested Fiat 3.4L. It's a good engine you can expect lots and lots of hours out of.
Yes, I like the electric PTO switch better than the lever PTO on the 75. Both are okay though.
Being as I don't do row farming, or much that is requiring that complex transmission, I didn't consider for very long, anyway, the more expensive versions. I do pasture cutting with batwing mowers, hay, plowing and using a ridged harrow, etc. So the more complex transmissions really bleed off for a payoff in the kind of work I do.
I shopped may brands and models before I got what I did. (The similar Kubota was more expensive, and very much less sophisticated. The Deere 5115M was a nice tractor, and I really liked it, but not $26k worth over what I paid for the PS120. The same held true for the T5's.)
Everyone has different uses for tractors. T5's may fit you to a T, but they can be quite a bit more money too.