So just doing some minor testing on lama. Results may be a bit incorrect.

+20 BAB Shurikens thrown with no boosts: 22 in 20 seconds (66/minute)
+20 BAB Shurikens thrown with haste boost IV+Ten thousand stars: 28 in 20 seconds (84/minute)

I feel like the bonuses to attack speed are quite a bit lower than they should be D: