The sendbug(1) utility provides a helpful fill-in-the-blanks form to ensure key information is captured, and it will automatically include some system information. You'll still need to add applicable Xorg logs.
Note that the bug tracking database is currently shut down. If you prepare a formal problem report with sendbug you will want to submit it to the bugs@ mailing list.
An informal problem report can be sent to misc@. There, you may find others with the same hardware who may be able to confirm your problem, or perhaps provide additional information.
Whichever route you choose, you will find both
http://www.openbsd.org/mail.html and
http://www.openbsd.org/report.html helpful.