I got 857.4G upon decelerating from over 15km/s to 300m/s in about 3 seconds. I admit I did not use only stock parts, but the only mods I used were Aerospike engine, Solar Collector and Radial-mount Parachute (total of 4 chutes for the deceleration). I can only assume the ridiculous G was from the deceleration rather than the 300m/s impact with the water a moment later. Also, here\'s a screenie: