I'm using an APC 17x6 on my Saito 180 with great results. In the past, I've used 16x8 APCs with decent results. Note: The Zinger wood 18x5 or 6 have a significantly larger diameter at the center of the prop (almost a 1/2 inch wider than the APC). I mention this because you'll need to accomodate this monster prop in a nose cone (I presume).

-Juhan