Windows Vista 32 bit vs 64 bit pros and cons

I am fixing to build myself a new computer once my tax money comes in. My major question is what would the pros and cons of having 32 or 64 on SL? And what are the known issues of having either?

i have 64 bit vista with 4gb ram
i have drivers for my components, nvidia, creative, etc..
SL is only 32 bit so it leaves 2 gb memory free all the time it could be using if it was 64 bit with object caching and view distance.
I haven't run into anything specific to 64 bit vs. 32 bit in SL but i've never run 32 bit vista with SL.

64bit - handles alot of ram.
32bit - max 3~3.5gig ram.

Thats about it, nothing diffrent nowadays, theres no reason not to use 64bit os anymore, 4 gig will fast become the minimum on games, oh right some already have.

If you use a 64bit program/client/games it will ram above 2 gig limit, so less loading, Hellgate was the only game i ever tried so far on 64bit, tried 32bit one and its utterly slow load compared.

SL is only 32bit & clunky client, so nothing diffrent on running in a 64bit os (xp / vista) then on a ordinary 32bit os.

Id' go 64bit either xp or vista anyway, more ram - less loading, not just on SL.

Thank you, this really has answered my question and has provided me with alot of information.