We maintain a list of external benchmark results here people have been experiencing to provide an idea of the relative performance you can expect from real-world usage:
Get 25k rows from MS SQL Express and convert to JSON​
EF & JSON.NET 2300ms
EF [AsNoTracking] & JSON.NET 973ms
EF [AsNoTracking] & ServiceStack 809ms
Simple.Data & JSON.NET 1598ms
Simple.Data & ServiceStack 933ms
ServiceStack.OrmLite & JSON.NET 405ms
ServiceStack.OrmLite & ServiceStack 245ms
ServiceStack vs WebApi client / server end-to-end results​
ServiceStack 9667ms
WebApi 30407ms
GitHub project for the benchmarks are at: https://github.com/anilmujagic/ServiceBenchmark
ServiceStack: a good alternative to WCF (French)​
ServiceStack 19s
WCF Data Services (Optimized) 28s
WCF Data Services 48s
ServiceStack.net​
One thing that I was completely surprised by today was the performance of the open source ServiceStack.NET frameworks. Even with the performance tuned release of JSON.NET I found that ServiceStack.Text beat it by a rediculous margin. It serialises 2x faster and deserialises 4x faster.
Redis vs RavenDB – Benchmarks for .NET Client NoSQL Solutions​
Redis (Cygwin) 254ms
Redis (Cygwin + fsync) 543ms
Raven DB 2983ms