So After connecting my PS Vita to my Ps4 and doing remote play with GTAO....it was great!
Honestly I had no lag, no hiccups, I was playing and running CEO jobs and had zero issues at all. It was literally like I was playing on my Ps4 but simply on a smaller screen. Also there was no noticeable framerate, honestly it looked like a more detailed version of the Ps3 version of GTAO being played in the PS vita. The PS Vita screen was beautiful but when in remote play the resolution is down scaled.
My only criticism (and this is me being picky) the text in the cellphone or menu texts (like the pop up screen when new updates come out) are small and kinda hard to read. And the controls can be hard tro get used too. the PS4 touchpad is touching the PS Vita screen. The pitta two back panels are used as L2 and R2 button respectively and the corner of the PS vita screen are used as the L3 and R3 (pushing in along stick). It can take time to get used to but you can change the button lay out to a more comfortable set up but after 30 minutes I was taking on the Los Santos police, enemy NPCs and some random players who attacked me.
Overall I would say playing GTAO on the PS Vita is 9/10 and great experience overall.
And a side note, this handheld is great I fell in love with it over my 3ds and even bought some games for it. The category of Japan imports are fun and unexpected!
Edit: All PS Vitas are region free, you can buy a import PS Vita (which have more colors and cheaper) and play/connect with your PS4 just fine. Any region PS vita will play any PS Vita game regardless of region. I recommended getting an import if you want to get a PS Vita.