Unlike child support, spousal support is often very difficult (if not impossible) to modify after the divorce is final, so getting it right the first time is a must!
On the other hand though, if you were willing to 'split' your retirement with her when the two of you retired as a married couple, then you shouldn't have a problem with splitting it up now, should you?
I know, it's not exactly the same thing, but that's how it works...
-------------------- I didn't get married to pay CS later in life.