I'd be inclined to just go for a Shrike upper. Good to have options, though.
The only problem with the Shrike is that it’s $3K+ and the waiting list is 5 years. Plus you have to put all your cartridges in the belt links manually (unless you have access to pre-loaded belts). The ammo box holds 200 or so rounds?
I’d just get two 100 round mags and save myself a ton of $$$. The Shrike would be fun though.