Azure Redis - How to select the optimal Tier for Production Nodes

Question

I have a webapplication facing performance issues on Azure Appservices. On running load tests , I am getting multiple redis timeouts.

I am using the stackexchange.redis library for maintaining session state and using Azure redis Cache C1 Plan. I wish to upgrade to C2 plan and running the load tests again. 

 

What should be the entry critera to select the correct Azure Redis Cache plan