> ... and inteldrm/radeondrm for a few years longer ...

Since many years longer, including the nv(4) driver for old Nvidia GPUs up to the earliest GTX models.

nv(4) is the old 2D user modesetting X driver (DDX), for legacy devices.

There is no kms drm or 3D acceleration for nvidia on OpenBSD.

How's the performance ?

Acceptable in my opinion.