If you're not sure if you're getting the best performance from your RC5 client, take a few minutes to benchmark all the cores to see which one gives you the best keyrate.

If you're in the "Core Throughput" view, go to View -> Console
Right click on the Console and go to Benchmark -> RC5-72 All Cores

This will start the benchmarking process for all the cores. Look at which of the cores will give you the highest keyrate.

Then, right click on the console again, go to "Configure"
Here choose "3" for Performance Related Options
Choose "1" for Core Selection
Set RC5=-1 to the core that performed the best.

Make sure you save your settings.