I think the question becomes, which is more important to you: shutter lag or wide angle.
With the 8700, you should have less shutter lag than the 5000 but less options for WA.
With the 5000 you have ~1 sec shutter lag but can use the nikon WA lens or a veriety of wetmate lenses from Inon or Sea and Sea.
The 5000 housing from Ikelite is cheaper (making the whole cost of a refurbished camera and housing the same as the 8700 housing).
With the 5000 you also get TTL. Ikelite is supposed to be working on TTL conversion circuitry for this camera but I'm not sure if it will be on this housing.
I don't think the extra megapixels is an advantage. More noisier pixels seems like a wash to me--except when it comes to storage. You get less pictures on a card with about the same quality.