Performance is an application specific type of activty. You will have a hard time finding a resource on the net that gives you a direct comparison of performance between the two. For features, you can look for something like this: http://db-engines.com/en/system/Microsoft+SQL+Server%3BPostgreSQL
For validation purposes, 'explain plan' is what you want in order to understand the performance of your application. Here are some quick resources to help you get started:
- Postgres - https://wiki.postgresql.org/wiki/File:Explaining_EXPLAIN.pdf
- SQL Server - https://www.youtube.com/watch?v=lH2_SI04PWQ
You can then compare the results between the two plans.