You've got to be comfortable with your particular numbers. The important concept is you're now in the game, plotting and planning to make ER your reality. I'm the same age as you, not quite 50, but knowing it's time to go. I've got a modest but rock solid Pension with Colas to count on, so SWR's are more of an object of study rather than worry for me. The "accepted" 4 percent rule seems pretty conservative, and obviously you'd never want to cut it so close that a few bad years would be even ablel to hurt you let alone do you in.
If you've tracked your expenses and are finding what you really need to live a comfortable lifestyle without risk, it's then a math equation about getting enough saved to accomodate or looking for less expensive lifestyle alternatives. I'm assuming you've looked at all those things, mortage paid off, moving to a less expensive area, reduced costs in a non-working life, etc etc etc.
Figure it out, make it so number one. I'm pulling out in 2006 at 51 come heck or high water.
It's about the music