64-bit-ness?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I'd like to switch one of my NetBSD/i386 machines to amd64.  There's
one that's known to run amd64, but it's not really very switchable at
present, so I was looking for another one.  I tried the most available
one and it simply reset as soon as the bootloader had loaded the kernel
off the install CD, so I assume that hardware is not recent enough to
run 64bit.

Is there an easy way to tell, given a root shell on a NetBSD/i386
machine, whether the hardware is NetBSD/amd64-compatible (or at least
64-bit compatible - I recognize there may be differences in supported
hardware and the like in corner cases)?  Looking at the list of
features reported for the CPUs on the one known-to-run-amd64 machine
and the one that isn't, I didn't see anything in the differences that
screamed "I'm 64-bit-ready!" to me.  My Web-fu is weak at best, but I
did some poking around, and my best guess is that features2 including
SSE3 is a pretty good correlate.  Might this be correct?  Or is there a
better test?

/~\ The ASCII                             Mouse
\ / Ribbon Campaign
 X  Against HTML                mouse%rodents-montreal.org@localhost
/ \ Email!           7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B