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I have a Q400S (only 1 hatch) in carbon/kevlar. The weight reduction was worth the cost, in my opinion, and feels significant. The boat is a pleasure to paddle, glides well, behaves predictably in confused water, is beautifully constructed, etc. It is a roomy boat - I am 5'9" and big, and there is plenty of room.
If you're shorter than 5'8" or so, I would guess the Q10X would fit you better. The only issue is the width - the Q10X is a scaled-down version of the Q600X, which is a performance model, whereas the Q400X is a general touring kayak. If you test it and are comfortable with the initial stability, it should be a great boat.
There used to be a Q300 model, which was a scaled-down Q400, but it's been discontinued. It was 13'6" by 24.5" wide. I recommend reading the model descriptions at Water Walker, as they contain the designer's statements about the various QCC boats.
PS Here's the Q300 page at QCC (even though discontinued):
If you're under 150lbs it'll be a BIG kayak. I had one, it's a good design, I'm not a fan of the seat and it's attachment though. I think of it as a good kayak for a 200lb person.
didn't reply earlier since it sounded like you were interested in the 400x
We have had kevlar 700's, 600's and 10X's, and right now I have a 700 Carbon/kevlar, and my wife has a carbon/ kevlar 10X.
If you are a decent paddler, and can enjoy a 21 inch wide boat, I suggest that you try both the 600, and the 10 x. The 600 might be a tad big for you.
My wife is around 116 and is 5'-2" and loves the 10x, (she was in on the design of it and had the first kevlar one that QCC built). She originally had a 600 and it was too big for her.
On the kevlar vs the carbon/kevlar I would never get a carbon/kevlar kayak again unless I was strictly using it for racing and was looking to shed an extra pound.
It is possibly because I paddle over a thousand miles a year in it, but from my experience it is too delicate, and I am constantly repairing both of our boats.
It is a big decision on your part, so good luck