Ain't no such thing as a free lunch. If you carry enough mags to feed your weapon through the day, and have them placed where they're easy to get at (i.e.: up front) then you're going to have trouble going prone. If you use high-caps you can get away with carrying only a few mags, but they'll sound like a maraca as soon as you fire some rounds, and winding them is a pain (it also exposes you...the winding mechanism on most high-caps makes a very distinctive sound). Sub-loads work OK, but limit how much you can carry.
If you're starting out, get the most basic rig you can find that will do the job, and expect to buy a better one later on (you can always keep the old rig as a loaner). Wear it, use it, and figure out what fits your operational needs. Then pick up a good rig once you know what you want. None of the teams here have requirements on what LBE you use, so get what works for you in the end. High-speed/Low-drag is how you perform, not how you look. As Murphy's Laws of Combat state: "If it's stupid, but it works...it's not stupid."
So endeth the lesson :-)
-Chris