We are developing a several web applications that use 'services' that
perform key business functions for our applications. These same 'services'
are avaible to paying clients through web services.  To summarize, we have
clients that use our web applications (they need UI) and we have clients
that just need the 'services' where they integrate our 'services' with their
applications through the web services. We have a single server that houses
both types of applications (we have failover). My question involves the web
applications and the 'sevices'. Should we use the web services from the web
applications or call the implementation components directly from the web
applications through their interfaces? My concern is performance for the web
applications and the fact the web services reside on the same physical
machine. It is argued on my team that calling the 'services' through the web
service allows for better stability and performance. I am not so sure.
Building a SOAP request and response along with the
serialization/deserialization would generate a large amount of overhead and
cause scalabiltiy issues during peak demand (which we will get). We are
document centric (not RPC) and deal with Xml streams, schemas, etc.

If possble, could someone direct me to some general guidelines or sites that
cover this topic. I have gone through Microsoft's Best Practices and
Patterns but nothing surfaced.

Thanks