I have used the XML approach to do some integration between databases. I would pass to an SP in a different database a set of reference numbers as an XML param and then join to that XML to the data in that database. Although this worked fine, when it started getting up to over 700 - 1000 records, I saw a major performance problem. It was very slow. Maybe it was my implementation, but I ended up having to rewrite it to eliminate the XML approach (which is what I should have done the first time, but I wanted to try out the XML approach). Just make sure you test your implementation using more data than you ever think you will need to process.