Thinking of doing our next project so that our logical tiers can be
physically tiered when desired for a given deployment and then not
physically tiered when that is not needed.  The solution, we think, would be
using WCF and when we don't need to physically tier use named-pipes as the
transport.

However there will be a slowdown because of the WCF marshalling and
seralizing compared to in-process calls.  My question is how much of a
slowdown will it be?