Now SP1 is for a time on the market and the release of the R2 extension for ConfigMgr it could be confusing which version of ConfigMgr is running on your server.

To quickly verify the version you're running in the ConfigMgr console expand Site Database and Site Management. Right-click your site server and the version number will be listed on the Site properties dialog box.

To following list will help you to determine which version number belongs to which version:
ConfigMgr RTM
4.00.5931.0000

ConfigMgr SP1
4.00.6221.1000

ConfigMgr R2
4.00.6221.1000

ConfigMgr SP2
4.00.6487.2000

Since R2 requires SP1 and it is extension instead of a upgrade the version number is the same as ConfigMgr SP1. Difference with R2 is that The “R2 installed” field will state “Yes”.