I think in one world with different landscapes.
From what I read the construction of the Saxony and the Deluxe Steel are different. The Deluxe Steel is said easier to open and clean, which I really like. And the mouthpiece the Saxony and Deluxe originally come with is different. The Deluxe has a rounded mouthpiece, which I also think I will like.
The other thing I read is that they are both excellent made instruments, the best of the Seydel range, very airtight (with the Saxony a fraction better) and having the same steel reeds.
(My little sister and I look and behave different, but we have many characteristics in common, and we are of the best quality ;-) We clearly belong to the same family.)