I received all parts earlier this week and put everything together yesterday. Everything seems to be working now, and the GPU is the bottleneck for gaming again (as it should be), while the CPU usage is below 50%.
I had a sound issue, where only the rear right speaker seemed to produce any sound. I spent roughly 15 min swapping place on the audio contacts and reading the motherboard manual, until I realised that windows had swapped audio output source to my recently plugged in headset (located near the right rear speaker). :-[