it will clip like any other device if the input level is exceeded (+4 mic +24 line), but yes in 32bit float, level control really does nothing and 'Full Scale' is pretty arbitrary. you can record something consistently over 0dBFS and the data is all there if you reduce the volume in software
this would be ideal to see these tested as stand-alone recorders in the same manner, as they are really same market segment
particularly if they were tested with mic level signals in the -40 dBV range typical of condenser mics
the mixpre has discrete class A preamps and I would expect it to shine in this application.
Both the mixpre and the zoom f6 have similar EINs but the mixpre can take a much hotter signal (+10dB on mic and +16dB on line) so perhaps it would make better utilization of the 32-bit float.
Sound devices also uses a completely different architecture for its multi-ADC implementation, utilizing 3 converters:
http://patentimages.storage.googleapis.com/a7/6b/f5/77e31e68cca8b7/US9654134.pdf