If a 13th lvl Sky Druid can already fly at 160ft [Into the Blue (su)], is that speed/ability retained when casting Elemental Body IV to become an Air Elemental?
If it's a class ability rather than something part of your form, then yes, sure.
Depends on whether the class feature depends on your form, which is GM discretion. Since it doesn't indicate the mechanism for your supernatural flight, it doesn't seem form-dependent to me. ETV.