Classic question which I suppose arises from that dilemma where you haven't topped up your account with miles transferred in for redemption.

Looking to redeem MEL-JFK return and for the dates I want, I can get MEL-HKF-JFK (CX) and returning JFK-DOH-MEL (QR). According to mileage monkey this return routing is 26,814 miles and so should fall in the 10k+ column of the award table and be 175,000 AM J return, with taxes being slightly higher for using QR.

Is that correct or is there an additional points penalty for using QR instead of CX on the return? I can't see anything on the award charts to suggest that but would appreciate clarification.

Also, is there any pricing consequence for having a HKG stopover oneway and I assume only available by phone?

175000 AM is correct, and yes I think QR has higher fuel surcharge. The downside of using QR is that, in case you want to rebook, the return has to be on QR and you cannot waitlist on QR. Waitlist is only permitted on CX.

On the other hand, if you can make your routing a combination of CX, QF, and AA (e. g., returning on AA+QF), and have a total mileage flown below 25000 miles, you can use the oneworld redemption chart and lower the price to 160000 AM.

That's an interesting observation about oneworld awards - thanks. Unfortunately no QF or AA available for my dates but will keep in mind for next time!

Just add a throwaway segment of QF to the end of your itin.

Right now OP's itinerary is over 25000 miles, so using the OW chart is going to cost OP more miles.