Not really sure what is the best option for you. 40hz is pretty low even for big towers. Best guess is either 60 or 80hz.
I have two very different sets of towers...
Gallo Nucleus Reference 3.2
B&O Penta
By shere/mere coincidence, they both provide good response down to 35Hz (both according to spec, and as measured during Dirac setup...)
In theory the sealed woofer of the Gallo's, can, if powered right (Biamping via its second voice coil), stretch down to 24Hz according to its specs.
I am not Biamping, but I am feeding the Gallo via a Crown XLS2500... 440W@8ohm 1200W@2ohm
Still the end result are I have two excellent tower speakers that both provide excellent bass down to 35Hz.
Getting below 35Hz (with any sort of substantive SPL) seems challenging with standard size towers
I would suggest, that for reasonably "standard" sized towers, somewhere between 40Hz and 25Hz is perfectly viable (based on my own experiences)
And there are therefore advantages to be gained from leveraging such "full range" speakers to provide excellent mid-bass... yes they are unlikely to extend into infrasonics... that would definitely require sub(s).
Any tower speaker SHOULD be "Full range"... and a full range speaker should extend down to 40Hz as an absolute minimum.
Speakers that are limited to 60Hz/80Hz are of course typical for the Home Theatre market (which is far larger than the traditional stereo market) - as they are designed to combine with an external woofer (most of which do no extend below 20Hz, so I tend to question the label "subwoofer"!) which will typically provide response from the mid 20's Hz through to around 120Hz
There are numerous excellent top of the line speakers from the 1980's, 90's and 2000's that can now be purchased for a heck of a lot less than their performance equivalents of today (the B&O Penta's being an example)... and these typically will have excellent performance well down into the bass region - outperforming in many cases, the smaller/cheaper "subs".