congrats on your new Renegade... i've mine since about when the Earth cooled, and it's seen a lot of use and it no longer 'pretty,' but still put lead on target when called upon to do so.
Mine is a flint, also .50 cal, and i've tried both FFg and FFFg (since i shoot flint, real BP is a necessity). Had better results with FFFg, but the distance between the two was not a 'train stopper.'
I would recommend that you get a pound of each and see what works best in your particular rifle. Each rifle will have its own likes and dislikes, and you don't know what they are until you try things out. That's part of the fun.
Additionally, if you don't already, get Dutch Schoultz' monograph. It's really money very well spent; helped my shooting a bunch.
Best of luck- make good smoke!