Today I was reading in Storey's Guide to Raising Chickens: 3rd Edition (Storey's Guide to Raising Series) by Gail Damerow
about the RIR and Barred Rock cross which they call a Black Sex-link or Black Star. Damerow said that this bird weighs in heaver than the Red-sex-link, and thus she says is a better meat bird, or "dual purpose" bird, than the Red. As the other poster stated though, these crosses are to get maximum egg production.
A lot of the existing breeds already are considered 'dual purpose'. Does FFA want you to experiment with existing known results or to find a new type of cross?
Good luck with the project it sounds very interesting. Post your results when you get them to help enlighten others about what you learned. Thanks.