Heavy materials are not the only way to make a rigid cone. The W7 gets it's cone strength from the shape (a deep 'W' shaped form) - not so much the material it made out of. The smooth parabolic dish you see on the face is actually a secondary cone for cosmetic appeal.
SQ oriented woofers with super rigid cones? Here's a few I could think of off the top of my head:
Polk Audio db series? (from the late 90's?) - the ones with the graphite composite cones...
Eclipse TI series (either aluminum or an aluminum composite, not sure)
SEAS and Elemental Designs also did some sort of composite metal cones at one time (may still?)
PPI Pro series (the original flat piston woofers, not the post-DEI junk)
Paper, as a cone material, is not the issue per se (it's a popular, inexpensive, and lightweight material) - it's the application of that material - and a floppy, deforming cone IS going to affect the quality of sound produced.
A paper cone 'can' also be a structural issue at far below than the power range or SPL levels you suggest. Case in point, the old 18" Strokers were known for creasing the cones on less that 3K - but admittedly, I would cite the shallowness of the cone as being the issue - not the material used.
Now I'm not suggesting people are tearing up cones on these little DD woofers - again - my point was for the same money, there's far better built woofers to be had.
How rigid is the cone on that W7? Find me a SQ woofer with super rigid (heavy) cone (Tc Sounds aside). Of all the reasons you wouldn't use that DD woofer for SQ the cone materials would be way way down on the list. I've used some soft dustcaps and noticed no difference whatsoever. About the only time it really matters is if you're running upwards of 8K per sub or are into the 170 dB range and need the extra strength to keep from shredding cones.Most of the hand built SPL marketed woofers have seen have ugly glue jobs.