I recently purchased a Martin Cheetah set at 50#/27in draw length.Included with it were the Beman ICS Venture arrows. The spine on these were 400, when I look at the Beman website it says in the chart it should be 500 spine according to my draw weight and length. Which is correct. I am shoot 100gr tips.
Sound stiff to me. I shoot 400 spines with 28" arrows (arrow length not draw length is the issue here) @60-65lbs with 90-100gr tips.
Too stiff tends to work better than too weak (and is safer). How do they fly?
If they tune right, give you good results and give enough speed don't worry about it.
I can comment from personal experience as I shoot a 27" draw and normally around 53# to 55#. Yes, you should most likely be shooting something with a 500 spine. And with the cam on your bow you should be able to shoot a 500 spine to about 60# or even a little more if you keep the arrows at 27" or less.
That doesn't mean that your 400's won't work. It just means they aren't the optimum spine. Were I you and given a choice I would take the arrows back and see if you can get 500's instead. If you don't have that option then shoot what ya got and be happy.