The following mods will be put on a Seadoo 2005 Sportster 150 jet boat (215 hp)

-external intercooler
-seadoo X charger
-4 inch intake

What prop would you recommend?

I can't give you a recommendation based on our testing as we do not test our parts or kits on sport boats. Solas recommneds a SRX-CD-14/19. Sorry I can't be more helpful. Maybe another forum member with experience modifying sport boats will post their findings.