In the past when doing enlargements, I had to adjust the time the paper was exposed when using RC paper and Fiber paper.

I will be doing some 8x10 contact prints soon, and was wondering if the same principal applies. If so, do any of you have a general rule on how much to increase the paper's exposure when using say, Ilford Glossy RC paper and transitioning to Glossy FB paper?

FB paper is very expensive so I want to try to do most of my experimenting with RC paper before making the final prints in FB.