Profile major aspects to ensure speed
One of the most enticing aspects about ServiceStack is that it is incredibly fast. I suggest that all major aspects of SS (web services, text, ormlite) get thoroughly tested in the upcoming versions just to make sure the code base is as fast as it could be.
v4.5.6 was a perf-focused release: http://docs.servicestack.net/releases/v4.5.6#performance-improvements
The benchmarks framework used to measure ServiceStack performance is at: https://github.com/NetCoreApps/Benchmarking