I recorded my screen while using the AppImage, and comparing it to the dev version (compiled today).
For both cases, I opened RT in METM, switched between the 2 tabs (File browser and Queue), opened a raw file, switched tabs to reveal the lag.
From the AppImage:
Screen cast AppImage
Initally, switching tabs is snappy. But after loading the first raw file, switching tabs is laggy (I hope you can see that in the screen cast). For some reason, at 1:25 the lag is gone, and swtching tabs is snappy again. At 1:40 I open a raw file again, and the lag comes back. Opening a second raw file makes it even laggier (more than 1 second I think). When I close the raw files towards the end, the lag goes away.
From the dev build:
Screen cast dev build
Pretty much the same behaviour, though the lag is much shorter (but still perceivable). Again, after a while the lag goes away (around 1:00 and 2:00 in the screen cast).
I observed the same important lags for the AppImage in SETM.