It is unknown what level of susanoo Itachi used ot tank Kirin.. However he tanked it due to Sasuke talking for 5mins before actually using it. He basically gave him time.
Also TBB and FRS are much slower than Kirin (Based on feats) Indra arrow was the same speed as TBB/FRS so it is much much much slower.. nothing in this series moves at .0001
Not really......Naruto's FRS and Juubi's Bijuudama have been calculated to be mach 300 and mach 4000 respectively. And there is no proof that Indra's arrow is any slower than Kirin. Btw Night Gai is the fastest attack, not Kirin. U_U