Here is what I will do. I jsut orderd 80 x 6970 to be delivered in slices over the nxt 4 weeks, as initial step.
* I will NOT use deepbit, too expensive.
* I will use a distributing proxy that distributes my load over 2-3 pools on a round robin fashion.
Why 2-3 pools? Because i like to reduce variance

Why not deepbit / pay per share? Because they charge me 10%. Why the heck would I dot that - thigns even out over 2-3 weeks anyway. I am in it for the money, not for paying 10% for smoothing my equity curve.
With that size of farm, there's little reason to mine in someone else's pool. You'll be bringing in 50 BTC blocks often enough that you won't really notice any variance.