Clyde, if you don't mind (you don't have to), could you test this: Breakout Championship/Rally Series. The 3rd race is in Hockenheimring/rain. Use Audi Sport Quattro S1, when it starts raining, go to cockpit view, race until the end in this view. When I tried it, I could replicate what is being said on that forum. It's not smooth at all, not 60fps smooth. I tried both cockpit views as well (both exhibit frame drops) and kept switching around views (other views were fine, smooth). Now, I'm not saying it's running 1 fps, but for this particular race, something is up. (I have a One S)
As for Forzavista, it's clear information is missing. Looking at the engine and hitting the info button produces absolutely nothing. No longer can the headlamps be turned on (unless in photo mode) and of course, the voice overs are gone. Downgrade if you ask me. To me, priorities were set to get this game out prior to 1X's release, so maybe it will be patched later on.
However, after playing GT Sport demo, its quite clear, Turn 10 can do a better job and take some lessons from PD on creating beautiful showrooms. Sure, voice overs are not needed and they became generic, but it was a nice feature. Scrolling information could replace that like GTS does and GTS does this for every single car, not to mention the historical aspects it also includes (pics/videos). To me, they know how to create proper showrooms.
Turn 10 decided with Forza 7 this whole car collection thing, so needless to say, it would've been nice if the encyclopedic aspect was applied for all these cars. Heck, with the specialty dealer, it would be great if they did.