I consistently travel the same distance faster in my Current Designs Extreme or Kajaksport Viviane than I do in my Capella 169 or VCP Selkie, as examples. This has been regardless of flatwater, 4-6 foot waves, wind, or calm.
I've seen a number of QCC's in this area. I was always surprised at the number that showed up to the Wrightsville Beach Challenge, a local race. I've never paddled one, but would like to give one a try. I never had one finish ahead of me, myself paddling a CD Extreme, Nigel Foster Legend, or CD Solstice GTS. But I've never figured that tells that much about how fast I would be in it. I'm no racer, and there are many much faster. I just have always figured the limit of my ability to make reasonable forward progress is the biggest factor determining the limit of the conditions I can safely paddle in. And I seem to favor kayaks that travel more efficiently when I start approaching 3.5 to 4+ knots, and that don't hit a wall when I have to make runs against currents.
I'm a fan of the CD Nomad/Extreme. I think it's a great kayak. Not a highly maneuverable kayak, but the positive tradeoffs are obvious and very appreciable when you get out there, and I find the maneuverability quite acceptable.
If you want a somewhat fast kayak with great maneuverability, and the size works for you (lot more room in this one than a Nomad), you should give a look at the CD Gulfstream. Rough water handling, and high maneuverability with lesser sacrifice of speed (compared to Pintail, Romany, Capella 169, Chatham 16). I think it proves too wide in the cockpit for many. But if you care about speed and a strong forward stroke, I think a good, necessary rule is to make sure there is a finger width between your hips and the sides of the seat. This allows rotation. And yes, you can still securely surf and play in rough water while allowing this important room. So if you're a little wider in the hip area than I, I think D-Hutch came up with something exceptional with the Gulfstream.
Of course, I cannot dismiss a report of a Chatham 16 not too long ago winning a rough-water race. Just how rough it was would have been fun to experience, and fun to observe in terms of the differing kayak's behaviors out there. As in all races, I also can't comment on the paddler's contribution vs the kayak, which is proven to be wildly significant.