I believe I have fixed all of my issues now as I've just played the game for well over 90 minutes without a single issue: performance was mostly solid even with 5 other cars on-screen holding 60 fps more often than not (only occasionally dipping to 52 fps intermittently from time to time), I have not been able to replicate the falling-through-the-road glitch despite using nitrous and loading times are now very quick after the one minute initial load. It takes around 6 seconds to switch between the garage and game now.
How did I fix it?
Well, on my system, I have Windows installed on an SSD. I have my games installed on 7,200 rpm mechanical hard drives that are obviously not as fast as an SSD but are still generally fine in terms of loading times (one of these drives is a 3 TB Western Digital Back). As the SSD is the fastest drive and I have 16 GB of memory, I thought I would only have a system managed pagefile on that and turned off the ones on the other slower hard drives. Well, it looks like this game has issues if you do that so I just re-enabled system managed pagefiles on all the other hard drives and that seems to have resolved the issue for me.
It may not fix the issue for everyone as they may already have these pagefiles but it seems to have done the trick for me so it is something worth checking IMO if you are experiencing this issue.
The game is still not perfect though: the engine hitches/stutters every couple of minutes (perhaps related to the streaming?) and shadow detail noticeably draw in at close range plus the transition between night and dusk/different kinds of weather is rather abrupt and unnatural looking (kind of unsurprising when this game has no actual daylight cycle). Finally, the city itself feels post-apocalyptic and devoid of life due to the lack of pedestrians and other traffic. Considering how Midnight Club: Los Angeles did this kind of thing over seven years ago with full day/night cycles, c-ockpit view (conspicuously missing here), pedestrians, 5X the traffic density and real-time cutscenes (not the cheesy FMV we get in this game), etc, etc, it's hard not to be a bit disappointed. Sure the game looks beautiful and closer to photo-realism but that all falls on its head due to the fact that the place you race around does not feel real.
A good game though but not a great one. Fun but ultimately flawed, like all of EA's recent NFS output.
