Ah, I see I've received the famous double post! Anyhow to further, some unofficial testing in The Witcher 3 at Ultra, no Vsync, unlimited framrate(minus Hairworks) settings I got the following:
1440p 99% GPU (afterburner), 70%-80% CPU
1080p 96%(dips)-99% GPU (afterburner), 85%-99%(spikes, mostly on Core#2) CPU, spikes coincide with GPU dips.
720p 96%-99% GPU(afterburner), 95%-99% CPU, all Cores, #2 pegged.
All drivers up to date, CPU @ 4.4Ghz, GPU at 1823Mhz boost, stable.
So it seems that at 1080p a minor bottleneck presents, you are correct. Also it seems Core #2 is slightly more loaded than the rest, its peaks were reflected in game as i little judder. At this time I'm assuming this may be the core used for physics as it definitely coincided with running, jumping actions onscreen. This definitely has implications for people running 144Hz monitors. I run 60Hz Vsync so it's no issue for me (yet).