Anything added to Banham will just seem more suited to Africa alive. I don't really understand why Banham ever introduced giraffe if competition with their sister park was ever an issue (although the enclosure is very good).
Now they have this species, I would suggest nothing they don't have already; use the large area to keep lots oF cranes, guineafowl, with a herd of grevys zebra (or exchange these for the Africa Alive zebra group), some eland, and maybe a group of camels, using dromedary in place of the current bactrians.
Someone made I think the best point already.....banham have historically been well-known for primates (although how successful they have actually been with them as opposed to having kept many species is another matter), and I think the fence could be electrified sufficiently at little cost for a large troop of vervets, or even baboons.
But what I would personally like to see is the existing black and white colobus group join the giraffe, some zebra, and the eland, with possibly a group of crowned cranes, depending on how much space and how many zebra and eland there are.