UPDATE 20/11/14 4:03pm: The final analysis is in. We've put together a wealth of GTA 5 clips culled from capture sessions spanning over 20 different missions, concentrating on areas where the title's 30fps target frame-rate faces its toughest challenges. In comparing PS4 and Xbox One, the end result is fascinating; it shows that while there are some scenarios that prove equally challenging for both consoles, specific areas can see one platform out-performing the other. On a native 1080p title like this, we might reasonably expect PlayStation 4's more powerful GPU to demonstrate an unassailable advantage across the game, but the reality is a little more complicated.
Travelling at speed through city junctions - such as Strawberry Avenue - turns out to be a particular Achilles Heel on PS4, with sustained drops to around the 24-26fps range at their worst. It's a situation that also applies to Xbox One, but to a consistently lesser degree when testing under the precise same conditions (and borne out in repeated tests). Put simply, in areas where junctions are stacked up one after the other, the Sony platform suffers more prolonged frame-rate drops when burning through traffic with your foot jammed to the floor. It's an interesting, recurring scenario that points to a CPU bottleneck, where Xbox One's increased clock-speed has an advantage when racing around these busy sections.
Another potential cause could be hard drive access, of course. GTA 5 is very intensive in terms of background streaming, a state of affairs that made the digital download versions of the last-gen version less desirable than the physical releases (where streaming bandwidth was shared between disc and drive). To lessen the impact of any streaming bottleneck, we installed the PS4 version onto an SSD for a re-test - the results showed no improvement.