Re: 399 GT-R34 question...
Well you could also see it as a good incentive to actually play NFS 2015 and leave Payback for a while. NFS 2015 has a lot to go for compared to Payback. Not that I find Payback a bad game, it has a lot going for it, but for reasons I often shut down my PS4 with the feeling the game could (should have) been better if one sees it as a follow up on NFS 2015.
NFS 2015 has freeroam cops, better story mode, better car custimizations.
Sure NFS 2015 can be picked up for a decent price if you don't require it to be brand new.