6.5X55AI vs 6.5X284 Build Questions

[m1a convert]

I have accumulated parts on my shelf over the years and I realized I basically have a complete rifle worth of parts sitting there. Here is what I have:

Rem 700 LA with .30-06 bolt face and oversized recoil lug
Bartlein 1-8.75 twist 27" Medium Contour barrel blank
Huber Trigger
20 MOA Badger Base
Manners Stock

I am trying to decide between 2 calibers: 6.5X55AI or 6.5X284.
Here's the questions:

1) It looks like they are close on velocity. Is this true assuming you load each to equal pressures etc?
2) I want to use AICS .300 WM mags on this. I believe that the 6.5X55 is finicky or won't feed from these mags. Which round is more reliable for feeding from AICS mags?
3) Is there something else I need to be aware of between these two? What direction would you go on this build?

 

[BigTex]

I can't speak on the 6.5x55, but my 6.5x284 has no trouble feeding from CIP length mags. It easily pushes Berger 140s 3050fps with H1000. I have had them over 3200, but accuracy wasn't as good. This is from a 26" Krieger Med Palma barrel. 6.5x284 is a nasty little round if you load.