sounds like you guys need to submit proper bug reports with detailed system specs either through the support portal or the forums bug section. Been playing since beta4 and never experienced these issues on my PC. My laptop either up until a few weeks ago (screen died on it... waiting to hear from Asus about repairing it). Granted, it is older hardware, but with reduced settings I am able to run upwards of 40FPS just about anywhere in the game (can break 100 at times, but I lock framerate to 60).
PC:
Win 8.0, 4GB DDR2-8800 RAM Intel E8400, Sapphire 5870 Vapor-X (forget if it was 1 or 2GB, but it is DDR5 I think). CPU and RAM are overclocked (430 FSB, reduced slightly because it's so @#$@#$ hot here atm), and the card had to be downclocked a bit too because of the increased ambient temps (air cooled)--but still slightly above stock speeds. Older Catalyst drivers installed... early 2013 if I remember right. They work, so never upgraded them. Basic rule of thumb with SE--when I find drivers that work, I don't change unless they stop working. They are infamous for not always working well with the latest and greatest because the games are bound to outdated DirectX methods that the new hardware/drivers/OS sometimes don't support very well.
Laptop:
Asus G75VX ROG model, Win 8.0, Intel I7-3630 (Quad), 8GB DDR3-1600, Nvidia GTX 670 MX with 3GB dedicated DDR5 RAM. Drivers are last ones I got from Asus to resolve some issues, version 311. Stupid LVDS cable got crimped internally and shorted--new cable didn't resolve it, so waiting on Asus to let me RMA it--may ned to replace the mainboard if it screwed up the port (everything works fine by HDMI out, but sucks to tether your laptop to a monitor to be able to use it--just been on the PC since this happened).
Both systems run full screen 1080p FPS capped to 60 to avoid the yo-yo between 40 to 100+) with at least 2.1 audio (laptop has a subwoofer built in, PC runs 4CH surround through an Asus XonarDX with GX extensions active--main speakers split off to a sub as a 2.1 setup)
Have played loooong hours on these systems with none of these problems (barring the PC throwing up on itself when the room gets too hot and I had to downclock things to make it stable again). Not talking 3 or 4 hours here either... I have kept my toon in game for over 12 hours straight (breaking off to tool around the house and such, but left character in game and all). It may not be a coding issue with the game per se, but more an issue with the OS's API's or the drivers. Perhaps a specific setting doesn't behave properly (like cascading shadows, or in game AA vs. driver level AA or something odd like that). So, you may want to provide a dump of your game settings and core driver settings as well to that end. SE may be able to better narrow it down if the proper details are provided.