TROW805 - 500 rounds of linked ammo will weigh less than the same quantity in box magazines. As to the reliability of either system, it depends on the system design. The best example of this the FN Minimi (the M249 SAW). When using belted ammo this system is highly reliable, but this same system is about worthless when using box magazines. Even if the gunner does everything right and prevents jams or feed failures, the cyclic rate is too high to maintain good suppressive fire 30 rounds at a time. The SAW is highly UNreliable when using box magazines. The powers that be tried creating a belt fed M16 variant at one time and it was a failure because the system wasn't designed to be a belt-fed weapon.
May your lead always hit center mass and your brass always land in your range bag.