These are all the medium ones.
Remember to right click and select Save As, name it EQUI_ShortDurationBuffWindow.xml or EQUI_BuffWindow.xml (depending on what you are downloading), then copy that .xml over to your UI directory. Don't cut/paste from your browser.
Short Duration (bard) buff window for 6 and 12 slots. Rename the appropriate one you want to use to EQUI_ShortDurationBuffWindow.xml:
6 Slot
12 Slot
Buff window for 15, 20, and 25 slots. Rename the appropriate one you want to use to EQUI_BuffWindow.xml:
15 Slot
20 Slot
25 Slot
htw