What is the difference between the seven and the ten qira'at in terms of soundness?

Question
Assalaamu Alaykum,

What is the difference between the seven and the ten qira'at in terms of soundness? I have heard that one can recite the seven in prayer, and the other three outside of prayer only but they are all mutawwatir. This doesn't make sense to me, as if they are all mutawwatir, I don't see how the three can be "less mutawwatir" than the others.

Answer
Wa alaikum assalaam wa rahmatullahi wa barakaatuh. 
There is no difference between the seven and ten qira'aat as far as soundness. The reason for "seven" qira'aat is that Imam Ad-Danee chose to outline the seven in his book: At-Tayseer, and Imam Ash-Shaatibiyy used the Tayseer for his source in his prose on the seven qira'aat.  Imam Ibn Al-Jazaree in An-Nashr, researched and took only the qira'aat which were mutawaatir at that time, which was 10.  The seven outlined by Imam Ad-Danee are included in An-Nashr. 
We can pray with any of the ten qira'aat and their various turuq. 
Wa assalaam alaikum