Going off TBB, a 200lb, 63" long, best quality linen string will be around 90 grains. Whereas for New Zealand flax you are looking at around 225 grains for a 200lb, 63" string. B-50 is listed as similar to best quality linen, but fast flight is about 40 grains for same strength/length string.
The values are rough estimates, but it gives a pretty good idea of relative strength per grain of weight.
I'd like to use New Zealand flax, I can actually see a plant from my computer desk
, but I can't see myself using it exclusively if it's requires 5 times the mass to make a safe string. I kind of want to make efficient bows as best I can, and if I know there's a component that's "dragging the chain", it will probably just annoy me, haha.