No, not the same, you mate Sebastopol to Sebastopol, where each are "curly", there is no sure thing as a "straight" feathered Sebastopol.
You can get different degrees of curl, from over curls thru to under curls. The curled feathers are very fragile so a over curled birds feather get damaged more and do not look as nice as long.
The so called "smooth breast" Sebastopol have less curls and lack the "look" of a Sebastopol, but as still "fully" blood Sebastopol.
So the mating of a over curl to a under curl "smooth breasted", you get a bird that will last long for exhibition that is all. Its feathers will last long.
With colour, the damaged feathers are less noticeable on the white, as for the grays, they look "ratty" all the time and do not present well, for this reason there are not kept for exhibition.
My two grey Sebastopols as "fully" blood Sebastopol as they came from two pure white parents, which normally produce white only. But last season (2007/2008) they produced two lovely girls.
IF someone tells you that you have a "straight" feathered Sebastopol, what you have is a cross breed, or some people call them "Ribbon" geese. These geese seem to only carry the curl on they shoulder and breast patches and none or very little in the wings. A true Sebastopol must have full curled wing feathers. Thus unable to fly, this is referred to as a "half wing". Ribbon geese curled feather seem to last longer than the Sebastopol, so remain "pretty" for longer, they also seem cleaner, as normal feathers can be cleaned, were curled feathers are hard to clean.
So to "hijack" your thread with this opinion, but back to your birds. I would have them in my flock (as I do) Ribbon goose or Sebastopol how cares, they are different to the "norm". And will look great. First it was Muscovies now it is geese, yes another person converted to "wet chooks" (Waterfowl)