200-300 rounds?
going zombie hunting?
ponder how you will use this setup, then assess REALLY how much sh** you'll be carrying on your person at a given time, compounded by whatever environmental stresses, logistical stresses, and limitations on PERSONAL abilities at a given time.
have you given very serious thought about how this load would be borne outside of going from the truck/PoV to a square range? What about other equipment? What are your limitations? Don't say that you don't have any, everyone will have some sort of detriment to their peak level of physical ability. Do you have any back problems? How is your range of motion? Any restrictions?
How is your range of motion when DIS-advantaged? ie. prone, on your side, on your back... with a large pack, carrying some sort of encumbrance?
the reality of the matter, is this type of topic is posted without *much* pre-ponderance by the original poster., those leaving the field open for conjecture / responses du jour and really leaving a end result which amounts to the same position as to which the original poster started out as.
Assess what you are PLANNING on doing?
What is your AO? Are there any AO specific issues that may impact your equipage?
Will you be traveling with others?
Are you physically able to maintain a sustain activity level over a certain length of time? Will an LBE set with aforementioned pockets become a physical constraint on your abilities?
How well familiar are you in weapon manipulation, magazine changes, transitiona etc? this will dictate what sort of pouch/equipment to invest in.
Are you running a sidearm? if so, will it be positioned in a manner similar to unencumbered carry?
-or-
you can just buy a few pouches, place your mags in them, and find out whether or not they work for you and be done with it and move on
BTW ---- functionality trumps LOOKS any day