Originally Posted by KMFDMvsEnya
Floorstanding speakers versus bookshelfs performance is highly dependent on the manufacturer's design decisions.
Both can provide great audio but as decent generalization a great pair of floorstanding speakers will provide better quality in dynamics, bass response, and output.
I do agree with this more refined statement. The question is whether this matters to the OP.
A bookshelf and tower costing the same, by the same company, will have differences. In the bookshelf, the manufacturer could afford to put better technology in, because it has a smaller cabinet and perhaps fewer drivers. The tower, even given the same sensitivity spec, has advantages.
Picture two people who are tasked with the new Olympic sport of Singing-While-Running. One is a more gifted singer with more experience and capability. The other, lesser singer, is a better athlete, who can run while tiring less.
If you ask the two to sing while just loafing, warm up jogging around the starting line, the first, better singer, will be judged to sound better.
While running slow at 10 mph, the first is starting to run out of breath, and it affects his singing. The second, being the better athlete, has no trouble singing.
At 20+ mph, the first is only gasping, and is falling behind. The second is singing as well (or poorly!) as he did at the starting line jogging.
The bookshelf and tower may even have the same rated sensitivity as eachother. But that spec is probably just at 1000 khz. At 400 hz, which is still well above your subwoofer crossover, the bookshelf might have trouble producing the same volume, IF pushed to high volumes, as the tower, with its bigger cabinet, and perhaps bigger and more numerous woofers.
So, if you play at medium volumes (more quiet than at a good professional movie theater), the tower has no advantage, and may sound worse. At high volumes, the tower will produce bass with less distortion.