It depends. Flemish are much larger, have larger bones, and take longer to put the meat on, NZs are smaller, have finer bones, and put the meat on quickly, so depending on what genes get passed on, you could get some fantastic ones or some really terrible ones.
I personally would keep the two breeds as two breeds, but if you want to try it, go for it If you did want to try it, I would do NZ buck to Flemish doe.
I'd try it, anything that ends up good (i.e the faster growth and finer bones in an otherwise flemish rabbit) you could keep to add to your breeding program.
Speaking as a mutt breeder, with meat rabbits anything goes as long as it makes you happy of course
Just remember, you could also end up with the opposite - bigger bones and slower growth in smaller rabbits
The University of Alabama and the University of Texas worked on a breed, mixing the Flemish, the NZW, and the Californian. It's called the Altex. You don't want to breed two Altex though. You breed an Altex with the NZW and you come up with what is called the Production White.
How did your breeding go? Did you get the type of kits you were wanting?
I did that and it worked out okay.
I want bigger size rabbits at butcher. I don't mind more bone mass.
As for length of time to butcher I don't think it took that much longer.
I am leaning toward going back to meat mutt myself for hybrid vigor. I've just about had it with purebreds. LOL