Most of the super-inflated breasts are filled with a silly-string type substance, not saline or silicone, and they are a LOT lighter than natural breasts.
Real or fake, big or huge, back pain seems to vary from woman to woman. I've known girls with DD-cups that just killed their back and shoulders, and I've known girls with HH-cups that they toted around with no problem whatsoever.
Miosotis is grand. In my opinion, if they're real they can't be too big. Milena Velba, Maria Moore, Eden Mor, Nadine Jansen... I'd take 'em all.