Microsoft has made some WCF performance data available on MSDN for a while now. The data shows the performance advantages of WCF over ASMX and other SOA frameworks on the platform. In general, WCF is the stronger performer--good news to all the folks who are currently implementing ILOG Rule Execution Server for .NET.
If you are deploying RES.NET using IIS 7.0 with Windows Server 2008, then you are no longer limited to the bassicHttpBinding. Moreover, the new architecture allows one to trim down the modules used by IIS--allowing for minimal features for your deployment. You can read about the new architecture here. If you want to read about the top 10 reasons why you should like IIS 7.0, then here is a link to a blog entry from Microsoft.com operations, "The Tasty Morsels Found in Dogfood..."