As far as I know, the Tyros5 uses the same great feeling semi-weighted FSX keyboard action, with velocity sensitivity and aftertouch, as Tyros2/3/4,
This FSX action was especially developed and used to provide better control of Yamaha's new SA/SA2 sounds.
The original Tyros did not have this FSX action; it was first introduced on the Tyros2.
The FSX action is also used on Yamaha's 61 and 76 key versions of the Motif XF, and the earlier Motif XS.
I believe you will find the Yamaha action comparable to what is used on the Korg PA3X.
The best action, in my opinion, for playing piano sounds, is an 88-note graded hammer weighted action keyboard, but for arranger playing purposes, the semi-weighted action works fine, and is better suited for playing the instrument's other sounds (strings, organ, brass, guitar etc.) than the weighted version.
I always thought that the Tyros FSX keyboard is not semi-weighted keys. I actually tried to find this out for sure, but not much information in internet searches.
My local music store rep was surprised to hear about the 76 note version Tyros 5, but agreed with me that the current Tyros 4 or 3 models are not semi- weighted keys.
My understanding is a keyboard bed and action in- between an actual piano and synth action. It would have weight to the keys like a piano, but somewhere in between. I remember trying out a 76 note midi controller keyboard with semi-weighted keys which I would find perfect for piano, but were a lot closer to an actual piano action.
I might still be incorrect, but maybe someone knows for sure. I do like the FSX action, coming from an organist background, and work very well for after touch control.
For me I would certainly go for the 76 note FSX version for home, and maybe in the future a 61 note version for gigging and backup.