Personally I?d split both the production systems and development systems between at least two different sites. e.g. primary for systems A, B, & C at location A, primary for systems D, E, & F at location B, and primary for systems G, H, & I at location C. Then have any secondary or backup systems at a location other than the primary.
As for the development, you can spread them out as you like. If they are truly used for development only then I?d have them closest to the development team (or at least the primary development team) for the systems on that box (I phrased it like that because I?ve seen companies use their development boxes to `fix? production issues on the fly).
I am currently working with a National client that has three data centers spread out across the US with similar configurations.