Honestly, 80-90# can feel a little light for carrying it on the shoulders and running, so I make the distances for the run longer. You can go for a while with 80-90#, like 400-800m per interval.
If you want a heavier burden run for a shorter distance (like 100-200m), then go for the heavier sandbag.
I think of the sandbag up to 90# for more metcon activities where the weight is lighter but you can keep moving and do more reps. For the different activites I use it for, the lighter sandbag suites my needs better. It feels too light for dragging (like this
- wfs), but good for everything else I like to do.