700mm. I highly doubt I could handhold a 700mm lens and get a sharp shot. I'm not knocking the lens at all. I might actually be interested. I just know my limitations.
Forget about your "limitations".
Optical stabilization plus IBIS are all you need. Depending on the speculations, they could allow a gain of up to 6-8 speeds.
So, no excuse to refrain from buying one...