I have kept gouldi types. Flavis, and crosses. Again I have never kept Savs but I would think their needs are similar. I know gouldi types are more active than savs and maybe eat more. Gouldi in the wild eat a lot of lizards and inverts. However, they like most varanids will eat anything, and do well on a mostly rodent diet.
Again I am no expert, so who am I. Just trying to relate what I know and help someone. If their is such a thing as a savanna expert ill let them take the wheel.