If it was made, a synthetic spidersilk suit of body armor would probably include a good deal of padding under the weave. As it would likely be difficult to pierce or slash through it, but wouldn't negate the kinetic energy of the blow, you'd be looking at blunt trauma. With the pads, it would likely mean you're getting some severe bruises, possibly even a cracked rib or internal injuries, but it beats the hell out of being dead. Note, however, that only applies to where the armor and padding cover.