I am going to be working on a 3d rainbow pegasus unicorn cake soon.  For the feathers on the wings....would cake lace or gum paste be better?  In my experience, gum paste in silicone molds is a huge pain especially when you need a lot of something.  I just wonder if the cake lace would work okay in a feather mold that is meant for gum paste or fondant.  

As far as using lace mix in a silicone mold, it should be fine...I use it in my Marvelous Molds Silicone Onlay molds without problems.

You will probably need to apply the mix in several layers and, depending on the brand of mix you use, air dry or oven dry it between layers. 

One thing about lace mix is that most of them are very flexible...some can be baked in a low oven to make them hard, so you might need to do this if you don't want the wings to droop. ...and be careful of humidity...lace mix will soften pretty quickly in humid weather.

Thank you Jeff.  I am in Alaska so humidity is not going to be a problem.  I will do layer as you suggested.  Wish me luck. :)