Does the world end if you keep both?
If dropping another iMac is viable then drop the 400 DV. Keep the 266 so you have a tray loader. The only iMacs I'm keeping in my personal collection right now are a Bondi Blue 233 MHz Rev A (the first) and a Snow 600 MHz (almost the last). If I come across a 700 MHz (the last) then I'll sell the Snow.
If dropping another iMac is viable then drop the 400 DV. Keep the 266 so you have a tray loader. The only iMacs I'm keeping in my personal collection right now are a Bondi Blue 233 MHz Rev A (the first) and a Snow 600 MHz (almost the last). If I come across a 700 MHz (the last) then I'll sell the Snow.