I've had an 8man kifaru for many years. I would not go smaller unless you do alot of two guys or less stuff, and/or are ounce-conscious.
As noted, the kifaru stoves are drafty. I switched to a one-piece, airtight, and love it.
My thoughts on seekoutside, FWIW, are that:
A, I would not hesitate to use one.
B, they are a new company and not "established".
C. The Kifaru design is such that
the many "panels" that make up the tipi have reinforced seams every few feet and so might be stronger and/or 'guys' could be sewn in at those points.
D. When seekoutside does get established, and if they start making bigger tipis, I'll probably get one.