I saw a blog somewhere stating Radeon fixed the reset bug in the 6000 series.
See:
https://forum.level1techs.com/t/best-host-video-card-for-passthru-support/184223/3
Only the 6800 cards seem to work perfect all the time when it comes to passthrough.
Various non-reference 6700 cards seem to have issues with the reset bug again, see: 6700XT - reset bug?. I forget if I’ve seen any mention of reference 6700 cards having any issues, but they seem to be working the best so far. My reference 6700 works great.It is highly likely that 6400/6500/6600 cards would also have similar potential issues and hangups as 6700 cards.