You really don't how well a guy's stuff will play up a few levels. For instance, not all 100 MPH heaters are created equal. Sometimes hitters at higher levels feast on breaking stuff that allowed a pitcher to plow through A ball. Sometimes at higher levels a slight lack of command becomes a tragic flaw.
I'd say hitters and pitchers generally face similar adjustment challenges as they move up the ladder. The next level always comes with the possibility of exposing your flaws. Pitchers, however, are vastly more likely to suffer a critical injury or to lose their stuff, which makes them a harder projection.