After re-fixing the bug I fixed before, and fixing the third one in the Sparc CPU emulation, I got Solaris 2.6 going. This version doesn't say how much did the clock gain since the release, so I can not estimate, how good am I doing in comparison to the reference 4900 days. Probably it was released in year 1997 on July the 18th.
SunOS Release 5.6 Version Generic [UNIX(R) System V Release 4.0]
Copyright (c) 1983-1997, Sun Microsystems, Inc.
NOTICE: SBus clock frequency out of range.
# ls -ld /a
drwxr-xr-x 2 root sys 512 Jul 18 1997 a
It also complains that
NOTICE: hsfs_putpage: dirty HSFS page
this may mean the current qemu workaround for non-emulating CPU cache is not good for Solaris. On the other side, who needs the hsfs module :).
Again, thanks Carey for the Solaris 2.6 disk!