The simple fact is that unless you're working in an exceptionally well acoustically-treated room you will always need to use headphones* to check your low end. At low frequencies the effect of the room modes, even if you've got reasonable treatment, will still be large. Using headphones takes the room out of the equation and allows you to make properly informed decisions about the bottom end.
Personally, I prefer a less-extended but more controlled low end, which can then be double checked on headphones, because it tends to make listening to the low-mids on the speakers easier.
So I'd err on the side of smaller speakers and put any cash savings to either a decent set of open-back headphones (if you don't already have them) or towards some acoustic treatment for the room.
This will, longer term, deliver a much better result than trying to get good low end extension from a budget (good, but budget ;) ) set of monitors in an untreated room.
* I tripped up on this a few weeks ago, I've got very used to listening on my monitors and hadn't really given a particular mix a proper listen on headphones - as a result I'd missed a build up of mush around 160Hz where my room has a null. Fortunately a fellow forum member pointed it out to me. :D
Ignore the post count, I have no idea what I'm doing...