400? No way. 340 might work, but I'd lean toward a 300 if you want to know the truth.
It might be worth it to borrow a couple arrows to find out what spine works best for you. They wouldn't necessarily have to be N-fused arrows, Just a couple 340 and a couple 300 spines to see which works the best. If the 340 tends to show a little on the light side you could always turn the bow weight down a touch. Something closer to 67# or so. You aren't going to be hunting anything that needs more weight unless you're going to Africa.
When tuning the limb bolts can be one of the most useful methods of getting good arrow flight, and they are already paid for.