Sally, if you like them you go for it

I only have experience with Wyndotte bantams that I use as Broodies, so not as meat birds.
Had LS and they were OK but a bit framey if you know what I mean, might have been able to improve them if I gave them more time.
With traditional breeds I think it's more about the strain rather than the breed, look for a breeder who breeds for DP and fattens his cockerels for the table.
Speckled Sussex will work just as well if the strain is right.
Either Wyndotte or Sussex should give you a half decent bird in there own right, I would choose your favourite and breed them for fast maturity and size, then have a few of the other hens to cross them with.
Always rear your crosses with a pure breed, then you can compare the difference between them and the standard bird and if it's worth it, like a control.
Will be a very nice project
