Wow,
That's a $50 dollar question. I have had both models in the past and liked different things about both models. I like the hull and deck layout (except for the angled hatch) of the X-Factor a bit better than the deck layout of the FnD. I especially like the smoother lines, the 2 inch mounting surface, and the sideways mounted smaller hatch that the X-Factor has. However, the X-Factor is a heavy kayak, and a guy I used to fish with told me that Malibu was changing who was going to be spinning their kayaks for them and he wasn't sure about the future quality of them, so he bought one before the switch. Now, this could be a just a rumor started by their competition, or someone doing it on their competitions behalf and have no real basis in fact.
On the other hand, Cobra spins their own kayaks and makes them in house. If you have a problem with one, you call them up and they take care of it for you. The design is older, but they still sell them by the truckloads, so how bad can they be? I had one of their FnD-XF models for a bit and liked it. I think it would definitely work out for scuba diving for you. But, if you're planning on taking an extra 72-80 tank with you, I dunno if you could slip it below deck through the middle hatch or not. The hatch may be long enough, but without doing it, it's hard to say. If one was on your BCD in the tankwell, you may have to rig up something to carry the spare in the bow area. With the X-Factor, you could probably slip it into the front hatch and down the pipe.
All that aside, I would really, really hesitate on buying ANY kayak sight unseen anymore from any dealer if there was a way around it. The only real good advice I can give is to paddle the actual kayak you're looking at buying, and if it feels good buy that exact one. Even though many kayaks come out of the same mold, they are a bit soft when they come out and can get bent a bit if the manufacturer is not careful or doesn't care about the quality, just the quantity pumped out.
If you do have to buy one sight unseen and have it delivered, don't sign for it until you have completely unpacked it and checked every inch of it. Once you sign that you received it in good condition, you may get stuck with a damaged kayak if you find damage after you signed. That's when buying kayaks online can get crappy pretty fast for all parties involved.
Hows the abalone diving going? I really dug the photos you posted before
Perry