It's very difficult to give a valid answer to this question....
Both companies are playing in the top league....quality wise, support wise and price wise. Both companies are run by very dedicated people who know what they are doing and will do a lot to support you. Both have sucessfully been used to carry a RED and to be honest, the frame is not the most important thing to consider. It's more the mix of motor, ESC, propellers, Flight Control and Gimbal Control....all this things will be your choice and can be done on both frames. I have no experience with the Skyjib, but with the Cinestar 8. My decission was based on the following facts:
After a lot of research I did not see any advantage of one company over the other concerning the frame, but I got the impression that the Cinestar 3-Axis Gimbal was a bit above all the other gimbals avalible. At that time there was already the first rumors about the RADIAN gimbal stabilization from Freefly floating around, and my impression was that if I choose the frame (Cinestar 8), the Gimbal AND the stabilization from one company it can't be a bad choice, since the development for the RADIAN obviously was done with a Cinestar 8 frame and the 3-Axis gimbal. It would be possible to mount the 3-Axis gimbal and the RADIAN on the Skyjib...the question is: what would be the benefits ?
In your case I would contact both companies directly, tell them what you are up to and ask for advice...ask them what they did to lift their RED's....you will need advice about the mentioned motor, ESC, propellers, Flight Control and Gimbal Control combination not only from users but also from people who develope this things.
Also try to download both building-manuals and study them and see what you "like" more.....
Chris