I have been thinking of switching to carbons for awhile. I've decided to take the jump. I am shooting a Martin DreamCatcher, 60# @ 28". I draw right at 28" and would like to end up with an arrow around 29" using 125 gr. BH's I'm planning on trying Easton Axis Traditional. What spine do I need? 400? Easton's charts say 340's but that seems too stiff to me.

I'd say the 400's will work. You may need a bit heavier point. You're right about the 340's being too stiff...unless you cut them long and shoot super heavy points...

I think 400s should be a good start.  Start full length and shorten 1/4" at a time until they bare shaft dead straight. Carbons shoot great, but to really dial them in they have a really narrow "sweet spot" for spne.

Easton Axis Traditional arrows come with a 50-75 gr. break-off brass insert.For me with carbon arrows to get one at a certain length is a hit or miss.Carbon arrows don't come in as many different spines as wood or aluminum.They react and recover quicker then other arrow materials.I would start full length with the weight you plan on shooting upfront and trim and tune from there.I let my tuning determine the final length of my carbon arrows.I don't even consider length as a factor unless they are getting too short.If you are just getting into carbon arrows you get get some GT blems from Big Jim for 1/2 the cost of Easton Axis,just a thought.But I would go for a .400 spine carbon arrow.Carbon arrows are a different learning curve.I  draw 27" and my carbons are from 28" to 30.5" depending on which bow I tuned them for.

It depends on bow, shelf, and length of the arrow. I would get a test kit. I have been shooting the axis for several years. I tried some of the traditionals last year and I found they shoot the same. I do the same thing Michael does. I tried the gold tips several times and I never could get them to fly. Rick Welch was a gold tip sponsor but he really liked my axis shafts. Now he is shooting a skinny shaft.

When I fiddle with carbons I shoot 400 ICS Beman from a 63# MOAB 29-30" arrows with 160 grain heads.
 

.400s should work fine. Cut them to the length you want, about 29 inches BOP and shoot. I recommend using the full 75 grain insert, or a 100 grain insert, plus aluminum adaptor and your125 grain point.

https://www.3riversarchery.com/SpineCalculator.asp?pass=2

This is a copy of the Stu Miller Dynamic Spine calculator.  Just fill in the info on your bow and run arrow choices.  Don't worry about the personal form adjustment.  Do pay attention to the window center cut and strike plate thickness though.
I ran your bow through as a Hunter and at 29 1/2" shaft, they hit the dynamic spine of the bow.

Thanks guys, I appreciate it.

I would go with the 400 cut to around 29-30 inches with that point weight.