Geez, that's a big topic. Way too much to be discussed in a thread like this. Here is a short version. Moving the forks effects a number of things. It is done to change ride height for one but the main thing is it changes rake and trail both of which GREATLY effect handling. This topic is not one to take lightly. If you want to do this you almost should get a book or talk to an experienced motorcycle suspension technician.
Not trying to dodge your question but again, the topic deserves more than what can be said here. Do your homework before you make such a modifacation or you may be sorry. You can sum up the issue like this though. High speed stability and quick steering response are really opposite things. The trick is to get a compromise of these two things and that is accompished by many things such as rake & trail, ride height, weight bias etc, not to mention the topic of suspension in general and the effects that it plays. It is a big can-o-worms my friend.