I would say that depending on the bow you could be either a little or alot weak for spine.

With a 29" draw, I would say that your arrows are probably in the range of 28.0" long (nock groove to end of insert/shaft
I shoot a Trykon XL at 65# and a 29" draw and those arrows would spine weak for my setup. I would shoot the 340s instead. If you are shooting any of the faster bows out there then you are probably in the same boat.

If you have an older rig, something with soft cams or wheels then the 400 would probably be fine.

If you post some more details, I can run the number through TAP (The Archery Program) and give you some recomendations on arrow dimensions that would spine perfectly for your rig.

Just a couple of things needed
Bow make and model
Limbs and cams
Draw Length (29")
Draw Weight (65#)
Fingers, or Release