On monday I upgraded cw1-hd6800 and cw2-gtx560 to Debian 9.4.
That went smoothly (unlike the vm1 and vm2 upgrade) and it does not seem to have upset the WineTest results much. If you look at the March 9 results you can see both the pre and post upgrade WineTest results (I reran the tests before the monday 12 commits).
https://test.winehq.org/data/dfde1195385df5ddb11f1104a0e744596b99477f/index_...
Only d3d9:device seems to have new failures, and only on cw1-hd6800:
device.c:1808: Test failed: The cursor handle is 0x10022
However this failure had happened on cw2-gtx560 before the upgrade so it's not entirely new.
https://test.winehq.org/data/661791cb7ea3757655aeff4fb061ada27a88cecc/linux_... https://test.winehq.org/data/acd2f1e59bd22197b63eb5ae4ac0d621a0b8cce0/linux_...
user32:win also has new failures but those started on the 9th before I upgraded cw1 and cw2.
The other differences I saw all seem to be related to random bugs that pop up from time to time. But now is the time to check for yourself.