Correct - heavier brass inserts are an option as well. 3 Rivers Archery has a spine calculator on their site that will let you plug in your bow info and help you get a feel how shaft length, spine and point weight, etc. impact the dynamic spine. It's helpful in getting to a starting point on how much more point weight or shaft length you'll need going from 400's to 340's.
I'm shooting bows in the mid-50 lb range with 340 spine shafts at 29" with 50 gr brass inserts and 175 gr points. How your sight window is cut is a variable in the equation also. I cut my sight windows anywhere from right at center up to 3/16" past center. Past center allows you to shoot a heavier spine shaft.
