The 740 estate has happily swallowed a double mattress (but so did a Rover 800 saloon) and various sofas but you can gain a few inches extra space in the 7x5 by removing the rear headrests and seat cushions - once lifted up vertically, they can be lifted out easily. The backrest comes out easily too, remove the "R" clip from the collars on the inboard side of the backrests where the hinge is, pop the outer pin out out and slide the outer edge forward and remove the inner end from the hinge pin. Replace the "R" clip in the collar for safe keeping, it expands when it's refitted so no need to worry about it anymore.
Also in my 765, i've shifted an Ikea 3 seater sofa with loads of room left. Granted it was disassembled into the back, base, sides and cushions but is well over 6'6" when assembled. Also shifted a DFS 2-seater recliner sofa which had to be carried in the reclined position due to the height of it.
As you say, swings and roundabouts on what you actually need to carry but more importantly, if choosing one as a load lugger, how often you need to carry stuff that would for example only go in a 240 - generally speaking the 7xx are more fuel-efficient than the 2xx so is the trade off worth it?
Against a V70, i'd say no, i'll keep the 7x5 even though it's juicier, against the 240, i'd still keep the 7x5 as the amount of times i'd need to move something that would only go in a 2x5 wouldn't justify the extra fuel costs in between.
Really is a case of "each to their own" and what suits an individual.
