Possibly a difference in monitor or video card performance? Hard to say. I'm also maxed on everything, but I dunno if that means my GTX285 is capable of doing everything I'm telling it to while my monitor is also a good number of years old and not HD.
Speaking of water rifts. Either it was the mobs, or do the rifts themselves create geysers that'll knock you around? Had it happen doing one in Moonshade, but didn't try a second since none popped near where I was questing.