The 20 fps locking issue during the bog combat scene in that Gamesyde stress test video appears, to me at least, to be caused by using double-buffering as it stays at that framerate regardless. If the game was not v-synced or using triple buffering then you would expect to see that framerate varying a lot more than it does there (it pretty much stays at 20 fps throughout with small dips above and below the line).
It is almost like the game is running with triple buffering outside of combat hence why we can see any numbers between 30 and 20 (sometimes less!) there but the engine switches to double-buffering, for whatever reason, in the bog.
Fantastic game without a doubt on both PS4 and PC (easily my favourite game of 2015 so far) but, in my opinion, no game in 2015 should be dropping down to 20 fps even if it is only for short periods in one particular area. CD Projekt Red should have optimised the game better in these locations, perhaps even used a dynamic resolution drop to 900p or whatever, reduced the transparency/weather effects, etc, to keep the framerate closer to 30 fps with triple buffering. It is not like they haven't had the chance to; this game has had seven patches on console!!!
