RC2 hangs on ACPI boot (ASUS a7n8x, nvidia)

I installed both 4.9 and 5.1 ok on my ASUS A7N8X (nvidia 
chipset) with AMD 2500 cpu.  After I cvsup'd to 5.2 a few
days ago, the kernel would no longer boot, hanging after:

Timecounters tick every 10.000 msec

Being new to the cvsup routine, I thought perhaps that I'd
made an error in following the notes in UPDATING about
installing the kernel and booting that before doing the
installworld.  So I downloaded the RC2 iso, made a CD and
booted from that. It hung on boot in the same place.

Booting with verbose logging gives one more line:

<snip>
procfs registered
Timecounter "TSC:" frequency 1837513615 Hz quality 800
Timecounters tick every 10.000 msec
lo0: bpf attached

Having seen other comments about nvidia and ACPI, I 
tried booting the CD with acpi disabled - and it worked.
I also tried booting my cvsup'd disk image without ACPI 
and it also worked ok.  

That leaves me with a system which requires manual 
interaction to boot.  One workaround that seems to work 
was to rename /boot/kernel/acpi.ko.  Not a good solution, 
as I expect that future cvsup/build cycles will eventually 
restore the acpi.ko file (and problem).

So... the point of the post:

1. The observation of this ACPI problem (might be related 
to others I've seen mentioned recently).

2. A request for a (cleaner) workaround to booting.  E.g.,
a way to disable acpi by default.

thanks for your help!
j