Portupgrade -af question

Okay guys, this is my very first post to the list, so please be nice to me. 
;-)

I have a simple question. I currently have FreeBSD 5.2-CURRENT #3 (from May 
9, 2004) installed on a semi-production server. I need to update it to 
5.3-RELEASE when it becomes available. I've read in src/UPDATING that all 
installed ports must be rebuilt (after a successful build world and install 
world, of course). Someone suggested to use 'portupgrade -af' to rebuild all 
installed ports. But this would take a whole day, especially since it's just 
a single processor Pentium III system. Shouldn't it be faster to let 
portupgrade use pre-compiled packages (either from a 5.3-RELEASE install CD 
or from a remote site)? Something like: 'portupgrade -afP' ? Would it work? 
This would save a lot of time... a lot of down-time, in fact.

Can someone more experienced with portupgrade confirm that this would work? 
I would really appreciate either a firm yes or a firm no answer. I just need 
to know the answer to this question from someone who is more knowledgable 
than I am, before I start doing something stupid... ;-) Thank you guys, 
all!!

Zoltan