Reducing the rake offset from 43mm to 40mm will increase steering trail and slow the steering a bit. This is exactly what I did to my 5500 Trek.
Adding rake offset reduces trail, and that can make the bike feel more twitchy, you're talking about going the opposite direction. Here are some links to help you:
http://traylorfwd.home.mindspring.com/geometry_def.html
http://www.kreuzotter.de/english/elenk.htm
Al