I've been using Great Whites for years,
but I've NEVER considered buying one. As a Pro using a piece of gear three (3) time a week means you should probably own it. If less, just rent as needed. As some-one just using a 400mm f/2.8 once or twice a year, renting is a no-brainer.
A hobbyist needs to follow a similar idea. Will you shoot BIF (or surfing, etc) every (or most) weekend(s)? Or will you just use it once or twice a year, while on a trip?
On one of the fora, about ten years ago, there was a guy who claimed to own every Great White except a 1200mm. He also claimed to have never opened a box (that would destroy their value). So are you a photographer or a gear collector (who seldom uses his gear).
BTW big lenses need big support, so you will need a
gimbal head or a
SharpShooter rifle stock http://www.sharpshooterindustries.com/ssHome.html Or maybe
both