First, to clarify, I was speaking only of armor panel weights, and was not including a carrier.
For III-A stuff, you could run two EXO's and a simple "throw and go" carrier. Total weight for two panels + carrier: approx. 2.5 pounds, for a rig that will repeatedly stop virtually all common pistol rounds. Of course, this is with 10"x12" inserts, rather than wrap-around armor, but they double as trauma pads. The Speed Plate is another option for this but I prefer the EXO.
For stopping three-to-four .308 rounds (but excluding M855 Green Tips), you could get the MASS III. Weighing mine, they showed 3.19 pounds each, so again - going with a lightweight carrier - you're in for about 7.5 pounds. Since the EXOs actually weigh in at about 8 ounces, that's 8.5 pounds total with both III-A and III standalone panels.
If it's important to stop M855, you will have to use something like the TAP Gamma or the MASS III-Plus, which are 5.5 pounds apiece. With almost all armor in the field these days, it all comes down to whether you're worried about M855. With virtually any brand or configuration, there's a 4-5 pound tradeoff between stopping them and not stopping them.
Edited to add: I did not see any specific reference to level IV when I posted about weight. If it was mentioned, I missed it. Apologies.