Just to add on to Jim's comment about Sony. I have the Sony AX100 which can record using the XAVCS format in an mp4 wrapper to SDXC cards at 3840 x 2160 without having to merge files. The AX100 does not have xlr inputs, but there are adapters like the Beachtek or, also, Sony makes a newer pro version (Sony NX80) that does have xlr inputs.
The problem I ran into with the AX100 was that Roxio didn't like its UHD footage. It would play the video, but not the audio. That may have been corrected in the most recent Roxio versions but I haven't tried recently. You might be able to get around that, because you can set the AX100 to concurrently record "4K" (UHD) and 1280 x 720. IIRC, Roxio accepted the audio from the 1280 footage np. (I'm not sure how Roxio would handle video from the NX80)
Anyway, just to say if the Panasonic doesn't do what you want, there may be another option