I have a 650sx. It has a 500GPH bilge that I flip on only when I need to (or on always when doing subs etc). I've had no problem with my ski even getting close to sinking. My hood seal sucks too. You don't really need to worry about sinking it. As long as your paying attention to how much water it takes in and making sure your getting it out accordingly, you'll have no problems.
Best way to sink a ski is to leave it unattended.
Just buy the ski, ride the ski, and keep an eye on how much water the bilge moves. Don't spend any money until the bilge is working over time. It's unlikely you'll need to do a hood mod as soon as you get the ski. Falling off wont sink it unless you never bother to get the water out, and you wont be doing many subs until after you've been riding a few hours. Just be careful if you decide to do a foutain.... You should buy a good bilge but wait on all that other stuff until you actually need it.
