Suppose you have a road bike with a top tube a bit short for you. The handlebar-to-seat distance should be about 25mm to 40mm (1" to 1.5") longer. You can either use a seatpost with more setback, or a longer stem. Current seatpost is an American Classic stem [edit: post] so I could get another 10mm or so with a different post. Current stem is a quill stem about 90mm [edit: 110mm], so I could get the whole 40mm with a 130mm stem, either quill or quill-to-threadless adapter + threadless stem.

Would you get it all from a 120-130mm stem? Put another way, what is the effect on handling of a looong stem? Or, would you go to the added expense of a different seatpost as well?