Todays value is debatable but I'll say this.
I own a lot of handguns, Ruger and others. IMHO the GP100 is one of the finest revolvers ever designed and the 4" model is so well balanced as to be near perfect. Add a bit of tuning, maybe along the lines of Iowegan's IBOK action work, you'll have a gun you'll never want to put down.
So Yea, if you can't afford to keep both, I'd grab a nice GP now, and worry about getting back into a 1911 later.