The often repeated mantra : "The Mission drives the gear..." is appropriate in this case.
IMHO, if you want to run four rifle mags, get a chest rig.
As others have stated, one to two rifle mags is about the norm for a belt. You could run three, but even if you are big (and have more belt room), that
is still getting a little crowded. Getting four on a belt is just going to over-complicate things.
I have three set-ups:
1) a battle belt w/ blow-out kit, tourniquet, dump pouch, two rifle and two pistol mag carriers, and a holster. I wear this during range sessions
and most training classes. I could wear this all day while doing training, outdoor work/activities, etc and be good to go.
2) an OSOE 'Micro-Rig' chest rig with hydration bladder. I wear this in conjunction with the battle belt for higher-speed carbine classes and such where
have more than a couple of magazines on your person is required.
3) the 'hyper-alloy combat chassis...' a molle plate carrier with plates, mag pouches, drop leg tactical holster, etc. The whole nine yards.
This is for shoot houses and those other courses requiring armor.
One instructor (former SF) told me that a lot of Tier One guys train with minimal stuff when just working on shooting proficiency. He likened it to a football team
practicing just in shorts and helmets.
Have some variety (budget permitting) in your gear, but starting with a basic belt and chest-rig setup will cover 99% of what you need.
Go over to the Tactical Gear forum and get a look at what others are using for belt and chest rig solutions.