Ohman! I missed pages of rabbit talk. XD
The FW's are slow-growers compared to the larger breeds, huh? How is their meat-to-bone ratio? I know it's pretty god on the New Zealands.
I raise the NZW's myself but I also have a standard rex and a giant mix and I had a cali cross at one point.
The cali was a little smaller but also seemed lighter boned. She was a NZW/Cali mix. My Rex is about lbs smaller adult weight and while her kits grow just fine, dressage ratio is WAY lower on them. My NZW's are real champs; 4lb kits at 10 weeks every time and the incredible part is I was looking at 75%-82% dressage ratios... If I recall average hovers at 55%-60%? Yeah. It's pretty great to have a 4lb rabbit and get 3lbs of meat off of 'em in ten weeks.
The problem with giants is not just the meat to bone ratio but also the SHAPE. Giants when they sit kinda tight look alright for a "meat" body... But when they're a bit more relaxed they are shaped like a burrito; all flat and long and low, at least compared to the high arch on a NZW.
If anyone is after some good production NZW's, I have some that were just born. We got 20 out of two moms a week ago. Great moms too, really strong instincts! We're expecting more later this month from some super awesome high quality rabbits too... Discounts to all my BYC friends. ;D
And as for natural feeding, Homesteading today has a great natural feed thread for rabbits... But to me it all comes down to one thing; hay, hay and more hay! All the hay all the time keeps bunnies healthy, and uh... Even more healthy.

I have kept rabbits for many years now and I cannot push quality grass hay enough! So many people flip out over how sensitive bunny tummies are but let me tell ya, I feed lots of hay and not a single problem with their digestives, not even when I was switching up feeds in a pinch AND giving sub-q antibiotics to one of my rabbits at the same time.
One of my favorite parts about rabbits is that I can use EVERY part of the rabbit. Heads and feet to the dogs, skin in a tanning solution, organs to the chickens... Everyone is happy with the rabbits around!