Do the "lift-support panels" really support D-cup breasts?

If you are a woman who has sagging then this bra is not for you. Zero support. The lift panels are nothing more that a couple of seams sewn into the cup.

I need. extenders to the bottom of the bra as on 44 c... i think a 42c would be a better fit with a extender to the hook and eye closure

All the cup size under DD should be normal and no extenders needed. I doubt if your real size should be 42D or even 42DD/42DDD but u don't know. I do recommend u go to the local store or mall to try 42D/DD/DDD to make sure your real size. Long tern wrong size wearing really hurts. have a nice day!

Does this bra separate the breasts, or does it give you a "uniboob"?

Based on our records we are showing this wire-free bra lifts and supports from the bottom to provide a superior shape and natural look. Ultimate lift support panels shape beautifully, making this comfort bra flatter your figure. Cushioned shoulder straps relieve pressure, and floral jacquard trim make this support bra look and feel terrific, and a soft nylon-spandex cup lining ensures gentle support.