The stress you can apply with clamping is probably greater because there is less of a negative effect on the other structures from the internal pressure, and the pressure is mainly just effecting the tunica.
I wonder whether that is correct since the blood vessels and NERVES are running right under the skin and are under high stress under a clamp. My personal impression and may be that of others (Mr. Happy, I think) would be that clamping is riskier than pumping but probably more effective (see the current poll I mentioned earlier, with a link).
Later - ttt