User blog comment:Xilinoc/Ch. 587 - The Headless Star 6 (for real this time)/@comment-11506376-20140703073433/@comment-11051098-20140704171612

Seeing as Shunsui said that the RG's total power surpass the Gotei 13, I think we can assume that the 5 ex-captains should be at Yamamoto's level, or close.

Yhwach is most likely prepared for their level of power anyway, seeing as he's had ages to spy on all the powerful Shinigami from the shadows.