Yes they do, its been shown many times. Just because your card can barely maintain boost clocks while at 90% average usage doesn't disprove throttling.
https://www.reddit.com/r/pcmasterrace/comments/4mlfme/_/
He returned his SLI 1080 because they were super hot and constantly throttled.
Here's my personal experience with 1080 SLi and Witcher 3:
- At 4k, Witcher 3 is locked at 60 fps 99.9% of the time. Mission accomplished lol. I literally skipped from area to area, testing with fraps. The only time is dropped below 60 is in the outskirts of Kaer Moren, where it dropped to 51 - 56 fps when fighting bears. I haven't seen it drop that "low" anywhere else.
- 1080s are WHISPER QUIET. Let me say this again...my 1080's are QUIETER than my 980 Ti's. Now, this probably means that my 980Ti's were working hard in Witcher and my 1080's do not have to work as hard, hence no need to ramp up the fans.
- Not sure how boosting in SLI works, but both cards boosted to 1886Mhz synchronized and stayed there. I played Witcher 3 straight for 30 minutes, no drop in boost (other than when I hit the menu button).
All in all, this was a terrific purchase for me.
Not sure why there is so much hate for this card. Half the crap I expected (heat, boost, fan loudness, etc..) didn't even come to fruition. Make that ALL the crap I expected.
There is a downside though:
- The 1080 SLi setup, not sure by driver bug or not, lost HDMI audio output on the 2nd card. That means I have to use optical audio out instead of HDMI audio, which is a real bummer. Will have to look into 3rd party solutions.