I'm not sure, but 50 lbs in 6 months with diet and exercise seems fairly aggressive.
Do you think you might achieve a better long term result if you looked at a year time frame and somewhere in the 15-1800 calorie range? Then you aren't strictly dieting, you are building a long term, maintainable, wellness plan.
I need to lose 15 for sure, I'd like to do 20...but my real goal is to improve my cardiovascular stamina. I took the kids out to the bush two weekends ago and I was flat-out winded walking quickly through rough brush. My in laws have 340 acres of bush and 4 wheeler trails. I want to be able to play all day on my kids level there without stopping.
My youngest daughter is in physical therapy and is supposed to jump as often as possible. I've started doing it with her in addition to my other exercise. This is shockingly hard to sustain for long periods.