You could always mix in some nubian or other early maturing breed. I say nubian because it is fairly easy to find a more meat or dual purpose type than other dairy breeds. I wouldnt add in a lot. Really, for the finished product if you will, I'd like less that 15% nubian. Just enough to add in growth rate. Honestly, the right boers could add size. Maybe use the bigger of the myotonics. They arent all super small framed. I think your really looking at more hybrid vigor with more breeds.
I love savannas and would like to incorporate them as well but haven't quite decided how or where