If I am in middle of Az Yashir when the Chazzan starts Yishtabach what is the right thing to do?
A) Continue on and answer Kaddish and Borchu and then finish Pesukei D’Zimra thereby being Mafsik between Borchu and the Brachos of Shema and also probably missing Kedusha of the Brachos of Shema.
B) Skip to Yishtabach and miss saying the whole Pesukei D’Zimra
C) Rush finishing Pesukei D’Zimra and hopefully getting Borchu and Kedusha of Shema
D) None of the above (and you have a better answer)
Thank you for your question.
If you are already in middle of Az yashir, (you already said Boruch Sheamar, and ashrei), then you should skip to Yishtabach to start Yotzer ohr right after saying borchu. If you can say Az yashir quickly, and still say Yishtabach before kaddish of course that is better.
As a side point according to a number of poskim, after one answered Borchu, he can no longer even say Yistabach! Therefore, it is better to skip and say Yistabach before the Chazan gets to kaddish.
Teshuvos Vhanhagos 1-89, Avnei Yoshpe (Tefillah) 8 Perek 5-6, M:B 54-14, Eishei Yisroel 16-35 ftnt. 104 in the name of R’ S. Z. Auerbach zt”l.