For stock ballast I'd run the 14.25x14.5 and with more than stock ballast I'd run a 14.25x14. Never checked the speed at WOT as we mostly run on a semi-private lake which is pretty small. We run a 2000 X-Star with the LTR 330 hp engine, 750's plumbed in the back, stock midship bag, plus one or two more 750's distributed depending (usually one in front of rear seat and one in the walkway) on how many people are in the boat.
My buddy runs a pretty similar set up in his 2006 X-1 with an RTP-1 310 hp engine. Changing to the 14.25x14 was a huge increase in hole shot from the stock. Can't remember what prop that was though, prolly a 13.7x17 or 14x18.