Assuming you lose 8 fps for the loss of 1" draw length and 7.5 fps per 25 grains of arrow weight:

70# at 29" DL with 350 grain arrow- 300 fps

80# at 29" DL with 350 grain arrow- 315 fps

80# at 29" DL with 400 grain arrow- 300 fps

80# at 29" DL with 440 grain arrow- 288 fps

Based on actual speeds posted by Bowtech design engineer Kevin Strother, these should be very close.