Never seen QR flight number appear on the QF website, guess you would have phone QFF up to make a booking.
From MEL, definitely go EK. The CX lounge is in the basement, same level as the MEL QFi J lounge.
One good thing about EK, is that the J/F cabins are upstairs on the 380, and no Y pax are allowed up there, you will never see anyone come up those hallowed internal (in the 380) stair case, so the loos are only for F/J passengers.
Edit: maybe because I don't have enough points and am only QF SG, J class classic rewards won't come up for me, when I do a classic reward search online.
NO EK/QR reward J seats, only CX/QF seats show up.
Better keep my dog mouth shut now, or I get into further troubles.
Anyway, whichever one you end up using, enjoy the flight.