Some quick -yet important- questions for AMD-64 as DB server OS

[Olaf Greve]

Hi all,

I have just been asked for my opinion/experiences in setting up a 
high-end MySQL DB server. Now.... I know some of the main things to look 
at, but I'm not 100% certain about some of the other things, and based 
on what I'll say they'll make their hardware decisions as well (and I'll 
be the one who will then most likely have to tune the OS and DB).

Unfortunately they didn't ask me this any time sooner, and if possible 
they would like to make their hardware choices today or on Monday, so I 
have precious little time to do the typical Googling and reading on 
forums etc.

Instead, I have a few basic questions, and based on the input I hope I 
can at least give them a hardware suggestion, and then I'll figure out 
the details when the machine is in... :)

Their questions basically come down to the following, and I hope someone 
can answer them for me:

1-What would be the most ideal selection of processor(s)? Would that be 
Dual AMD-64 (Athlon?), Dual Xenon, or Dual core AMD-64? Also, generally 
spoken what is better: two AMD-64s or one Dual core AMD-64?

2-Does anyone know if the MySQL versions that appear in the amd64 ports 
are specifically tuned for the AMD-64 architectures, or are they not a 
whole lot different from the normal -say- i386 ports versions? IOW, just 
"how 64-bits" is the amd64 version of MySQL?

3-Which MySQL version (generally spoken) nowadays has the edge for 
performance (under the amd64 version of FBSD), would that be 4.0.x, 
4.1.x or is 3.23.x better for speed?

4-Does MySQL have explicit tuning options (e.g. in my.cnf) in order to 
specify the amount of processors to use, or is that automatically 
handled by the OS?

5-The people who asked me this are very W*nd*ws minded, and I am not. I 
told them that IMO it would be far better and easier to tune a MySQL DB 
under Unix than under W*nd*ws. Can someone please give me a good edge, 
for this such that indeed they will NOT want to opt for W*nd*ws, or am I 
totally off-base here and can the W*nd*ws versions of MySQL be equally 
well tuned as the Unix versions for a high-end (!) DB system?

6-Any pitfalls you may be aware of when using the amd64 FBSD version for 
a high-end DB server?

Thanks heaps in advance, and cheers!
Olafo