I'll be ordering the 2200 bag tomorrow! Woohoo! Looks like a really nice and streamlined design.
Started doing weighted backpack training with my K4 5500. So far, just one sandbag in it.....so total pack weight is a bit over 25 lbs. Carries really nice! Got two more sandbags I can add which will take weight to a bit over 40 lbs and 55 lbs. Plan to bump to 40 early July....then maybe 55 in August. Progressive resistance and all that. Bought some inexpensive workout sandbags on amazon and some play sand at a local big box hardware store for this.
Sandbags, if you are interested:
https://www.amazon.ca/dp/B091BVL8WM?psc=1&ref=ppx_yo2ov_dt_b_product_details Just using the three smaller ones for now. Work great on the K4 load shelf.