The 857 that you listed from wakeside is only half way between your stock and the 14x14.25 as far as performance goes. It will be an improvement from your stock prop, but it won't be the night and day difference that we're talking about.
You can find them much cheaper than Wakeside. Delta props (formerly propellersonline.com) has them for $475: http://www.deltaprop.com/shopdisplayproducts.asp?id=238&cat=%2A%2AOJ+XMP+Ed ge%96+4+Blades+%28Tapered+Shafts%29%2A%2A
You can also get a great deal from Skiertoskier.com However, you'll need to e-mail them first and ask for a price list. I basiclly did some shopping online to find the cheapest price and then found a local dealer to match the price.
You should also contact Eric at OJ props to get some advice as to the exact model that will best fit your application.