Get the job done fast! While your drive is in transport you can access the full collection via 2k ProRes downloads. That way you can get started working immediately after purchase. In most cases the 2k downloads will be more than adequate to create finished professional shots. However, in cases when 2k simply isn't sufficient, you can still use the 2k files as proxies or placeholders until the higher resolution files arrive via hard drive.
With the R3D files on the hard drive you'll have full access to the original camera files and all the extra resolution and color depth therein. If you have your own workflow and keying techniques then the R3D option is for you.