It looks like it's going to be fast and the numbers look good at 4 and 4.5 knots. You'll get a little less resistance at 4 knots if you get your Cp down to .53, but you're going to lose some volume in the ends. If you're trying for 5 knots, you might try getting the Cp up to around .56 or so to see if you gain efficiency. It's pretty narrow upfront, so it's going to dive in waves and not come up quickly, which could slow you down. Get some flare up there above the waterline to help the front stay dry and keep up some speed. I'd consider changing the shape of the bow to something more similar to the Rockpool Taran (http://www.rockpoolkayaks.com/taran.php) to get a touch more waterline and more volume up there.

I'm not sure I like the look of the rocker forward the cockpit. It just doesn't look right to me. I can't put my finger on what I don't like about it, but I'd mess around with it a bit more.

My guess is that it's not going to have a high primary stability, but have good secondary.

The lines for Epic's 18X Sport are in the October 2008 issue of Sea Kayaker. I suggest looking at them a bit if you haven't already.