Good advice quoted above. More so if you are accustomed to practicing with that GP100. I've never placed any premium on lighter and lighter weights for J Frame revolvers. Nevertheless I do own one and it does serve a purpose. It is what it is. Someone on this very forum once commented..."A gun to carry when you can't carry a gun". You can expect reasonable accuracy at the distances the gun is made for and you can't argue with the carry comfort and concealability.
Have you had a shooting session with an ultra light? If not, make it a point to do so before buying one. It may save you a costly mistake.