I've had both the Tyros 4 and still own the S970. I gigged with both over the past few years.
The Tyros has a great sound and controls for live play. The S970 has a good sound and a much lighter footprint to carry around.
I'm currently gigging with a Korg PA 4X. Has the controls(+) and sound of the Tyros but also has the size and close to the weight of my S970.
If Yamaha ever produces a Tyros similar to my Korg PA 4X, I might switch to that.
What i like about the T4 is the SA2 sounds, the keybed, and the layout of the buttons...
What the 970 has to offer is lower weight, and personally i think the 2 knobs, with arpeggios and deejay styles really are a step forward for anyone that also needs to play some 2016 dance music..
I agree with you on the pa4x... However, comming from the T5, there are also some things i will miss of the T5 when deciding to go to a pa4x....