When testing different IR's, I just open a second window of RM. In the first window I choose my rigs and in the second window I have my IR folders.
When double clicking on any IR in a folder it loads instantly into the cab section of the rig chosen in window 1. So you can try out IR very fast by just going through the IR list.
I found out that there's no need to open a new window. Load up your preset, then go to your IR folder on RM, simply double click on the IR you want to try out. It automatically loads that IR up on the cab.