Ultimate Warlock 210 lxi Prop Help

Hello everyone, I have a 1996 Ultimate Warlock 210 LXI Big Lake that has a 383 stroker and a Alpha one gen 2 with a 1.47 ratio. I had purchased a nice power tech 4 blade 15.25 x 20 from my local boat shop and well i was at the lake doing around 40 and the boat acted like in went into neutral.. i went back to have a look and the prop and the shaft are gone.. It sheered the prop shaft off at the seal. i was amazed cause this is a brand new outdrive. So i got the shaft fixed and know im back to finding the right prop..

Here is my data on the 15.25 x 20 power tech OFS4:

WOT 5100
MAX SPEED 60 MPH
HOLE SHOT FAIR have to trim up a lil to get it going..
BOAT WEIGHT IS 3300 LOADED

DATA ON THE MERCURY NEMISIS 14 X 23 4 BLADE ALUMINUM

WOT 4700
MAX SPEED 58
HOLE SHOT CAVITATES

Boat shop told me the shaft broke because either the prop was loose or it was a defective shaft. I don't know ???

If anyone has any insight to the right prop for this boat I would greatly appreciate any and all help. Thank You Michaelv

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Ultimate Warlock 210 lxi Prop Help