Scenario 1
Mastery - 65%
Haste - 50%
1.3 s cast
462 casts
first 5 frostbolts yield 500k + 5 x 65k icicles stored.
FB 6 and every FB after yields 165k total dmg
That leaves 457 casts less final cast (below) 456 casts.
on cast 462 release 1 FB and remaining icicles for 425k.
total damage is: 500k + 75,240,000 + 425k
76165000 over 600 s - 126942 dps.
Scenario 2
Haste 63%
Mastery 45%
1.2 s cast
500 casts
first 5 frostbolts yield 500k plus 5 x 45k icicles
FB 6 and every FB after yields 145k total dmg
That leaves 495 casts less final cast (below) 494 casts
on cast 500 release 1 FB and remaining icicles for 325k
total damage is 500k + 71,630,000 + 325k
72,455,000 over 600 s - 120758 dps.