You never want to be running the PSU near it’s max rating. Some very simple math says that 700 would be 70% of the 1kw PSU, which I think is fine. But, I’m not sure that I’d put much more of a load on it. With how quickly you seem to outgrow your systems, you might be better off with the 1200w PSU. Either that, or get a case which can hold 2 PSUs, like my Lian-Li does. Then, you could get two smaller PSUs and still have quite a bit of room to grow.
