Not personally familiar with the products, but the rep is good. Sale ends 12/22. Click banner at top of site and submit e-mail for free shipping.
Looks like the Rush72 has what seems to be some sort of load-bearing waist belt. Smaller packs on "Sale" might have buckles on their lower sides for add-on belly bands, which provide pack stability during vigorous movement, but carry no load. No mention of included frame sheets in any of the packs. May be included, perhaps not. The larger the pack, the more it needs a frame sheet; Even small packs can get good benefit from a frame sheet. If packs lack some sort of frame sheet, make your own out of 1/16" thick black HDPE sheet from Grainger's. Round off the corners, and sand the edges of the sheet so there's NO sharp edges or corners that will cut/abrade the pack fabric. Smooth is the operative term. Or buy one of the right size.
Use banner at top to submit e-mail and get free shipping. Un-subscribe when it suits. Take a look at the compatible pouch page and load-up with compatible colored pouches, and also look at the Rush Tier system that allows attaching a smaller pack on dorsal side of larger pack. Questionable (IMHO), because it sacrifices stability by compromising user's center of gravity, but it's an option, perhaps for a small pack with light items. Bundle and save on a single order with the free shipping.
As said, no personal experience with the product, just going on their rep.
Disclaimer; no financial interest.