A stop loss can make some sense - if you"re losing it could be variance, but it could also be that you"re being outplayed and/or tilting. Not losing more than a certain amount could stop this damage before it gets worse.
A win limit makes far less sense - if you are going to throw away money you"ve won, then you should stop the moment you feel you"re not playing your best. However, if you"re beating the other players, then every minute you"re at the table you"re earning money, whatever the variance is doing.
Why not set a time limit for the amount you play, rather than a win target? Then, win or lose, you have to stop at a certain point. It will stop you chasing targets you might not be able to achieve, and give you the discipline to accept short-term losses as part of the (very) long term plan.
Ultimately, I guess monetary targets don"t help in poker the way they do in shares. You could play the same session the same way - one day your three flush draws come in, the next they don"t. In the short term this is beyond your control - in the long term, as long as you"re playing the odds correctly, it is in your control.
Hilger"s Inside The Poker Mind has a long discussion about this. Also other poker psychology books, no doubt.