It sounds like there's a tone of wood in the kitchen already. I'd do something different on the island, like a painted finish in a neutral color (gray, black, cream), and find a complimentary countertop material but something different - maybe a beige marble like Botticino. But I'd go for something with contrast.
Good luck!

Oak changes color as it ages, so it would be difficult to match your wood tone exactly - and as Rebekah stated, you have alot of wood already.

Why not take the opportunity to add some color? You don't have to stick with Black or White - why not consider a nice Fern Green, Indigo Blue or Barn Red?

...as far as your counters: If you select a different color for your cabinets, you might as well do a different countertop material - It makes more sense since it's been added over time to do so. You could do Soapstone, Butcherblock, Polished Wood Planking, Stainless Steel, Copper, Zinc or even Tile!