Just a friendly reminder that B-trees are often faster on modern microprocessors than RB-trees. See kbtree.h for a simple, yet fast example.
I didn't test it, but I'd assume B-tries would be rather efficient.
Red-Black trees are isomorphic to B-trees of node size 4. If you take a Red-Black tree and put each black node together with all its red children into a single node then you get a B-tree of node size 4. An insertion/deletion algorithm for Red-Black trees gives a corresponding insertion/deletion algorithm for B-trees of size 4 and vice versa. Putting those nodes together in a single node probably improves performance already because you have fewer pointers, and you can improve performance further by increasing the size of the B-tree nodes to, say, 32 instead of 4.
They are isomorphic, but B-Trees are more cache friendly. B-Trees store more in each node, while red-black trees require pointer chasing for each element.