What parts of disk geometry are relevant?

I'm setting up 5.1 with a couple of new drives.  Sysinstall, and for 
that matter,
any combination of command line tools, all seem have different ideas 
about
geometry. Sysinstall would use any of the numbers I threw at it, and
even after using sysinstalls values, fdisk and bsdlabel find reasons to
gripe.

Configuration data:
The geometry from the manufacturers docs, which is reported several
times at boot, is: 152627MB <ST3160023A> [310101/16/63].
The geometry mandated by sysinstall is: 19475/255/63
(The drive physically has 2 platters and 4 heads - but at least 16
is a multiple of that)

Both sysinstall-help and most of my web research says that the
way to be sure about what to use is to boot to dos or windows and
see what it says.  That is hardly convenient as my only use of Intel
based systems has been confined to {NeXT,Open}Step and now
FreeBSD.  What does DOS know that FreeBSD doesn't?


I'm migrating from a 2+ year old 5.0 installation, which is in 
production
use, so I don't have the luxury of just playing with the parameters to
see what boots and what doesn't.

As far as compatilbilty goes, I need 5.x BootEasy, the loader, and the
kernel to be happy about all the slices+partitions on the drive.
If there is any difference, Compatibility with 4.x as well would be
nice but is not required.

I'll ask two questions first, since yes answers will relegate the others
to matters of idle curiosity.

1. If newfs succeeds for a ufs2 partitions extending beyond 120GB,
does that mean the configuration is OK?

2. Is sysinstall's cryptic refusal to use the reported values, (and 
astoundingly
poor choice of alternate values), solely to ensure that Wintel OSes 
sharing
the drive don't get confused?
(c'mon 255 heads? And don;t get me started about a cylinder size
whose factors  are all prime!!)

If the answer to either of those is no, I would appreciate further 
clarification.

The rest of my confusion surrounds related issues of geometry, and
whether or not they are important, or irrelevant.

The original design of ffs/ufs mkfs was heavily dependent on geometry
for performance and reliability.  These are memories from v7, but
I seem to recall that rpm, skew factors and interleave were important,
and that incorrect vs. correct values had significant impact on both
performance and reliability.  bsdlabel -A reports 3600 for rpm (a very
old default) interleave is 1, and the rest are 0.  Are these just legacy
structures on disk, or is anyone paying attention to them?

Fdisk reports cylinder numbers which obviously depend on the geometry
used when the partition (slice) was written.  It always complains that
the in-core disk label will not work beyond cylinder 1.  Is this more
pandering to DOS or can I ignore it?

Bsdlabel complains about c partitions not covering the whole unit.
I checked and found that sizes of all defined partitions sum to c, and
that the size of c equals the size of the slice reported by fdisk.
I checked the code, and it seems to be saying that by 'c' partition
in a slice doesn't cover the whole drive.  In that case, the warning
just seems out of place. Is that what's going on?