Remoting vs. Importing XML

When should I start considering remoting over generating XML from a database and importing it? I have a large project going on right now that will be hit by as many as 500 people at once during certain parts of the year. I started off not knowing a thing about remoting, so I build it all around importing XML. What type of performance difference would I see between the two? Based off this usage level, should I go the remoting route?

I have been messing around with amfphp. It stinks that it doesn’t support E4X yet. Or is there something I’m missing?