I've never tried to max out a frameless pack. I recently did a five night trip around 25lbs when starting, and that carried comfortably. If I wanted to go out for longer than that, I would probably carry my ULA circuit--not so much for weight but for volume, as I find larger volume frameless packs don't carry so well, and greater weight usually translates into greater volume.
For me, the key elements are (1) a tight vertical column of gear (I prefer the rolled pad method), (2) wide, thinly padded (thinlight) shoulder straps--at least as wide as GG straps and (3) a wide thinly padded hipbelt (e.g., mountain laurel designs). With these three features, I've found a frameless pack will carry as well or better than any framed pack I've used.