OP
Update: Just in case anyone other than me is actually interested in the verdict. 
I went to another LDS and tried on size 9 Rockboots, with my Thor-Lo socks only, and put on a pair of XL Jets. They fit. It was tight, yes, but they fit and did indeed go far enough in to be fully useable. Note that I was NOT including the suit's sock in the shoe, which would have made the shoe a tad bigger and may have prevented it from fitting. But I think it's clear that: 1) people with size 9.5 feet should not wear size 9 rockboots, and 2) people with smaller feet than 9.5 may be able to get away with it. I figure the suit's sock adds a half to full size, so people with size 9 and smaller, who are satisfied with the insulation provided by Thor-Lo heavy trekking socks, can probably use size 9 rockboots with XL Jets.
Photos (excuse the crappy cellphone camera):
At first glance it does not appear to fit:
But pushing it in, realizing the shoe material wraps around the foot, perhaps it does fit:
Putting the shoe on, however, and actually wearing it normally, and while yes it is a close fit, it fits:
From the top:
The last part of my test was trying the 10.5 Converse in the XL Jets. I didn't have a drysuit's sock at home to test with, but I doubled the Thor-Lo's, which should be about the same thickness, to simulate it. It fits nicely, except it is pretty tight on the side where the extra bumper rubber is. I think shaving that rubber down slightly would do the trick, as the person mentioned doing with the size 11 Converse to accomplish the same thing. Note that my springs are pretty stretched out, but I think it'll get in tighter once I shave it down a little. And it still gets enough of the foot in the pocket to be considered useable, IMO.
Photos:
Side view:
Top view:
Bottom view:
I went to another LDS and tried on size 9 Rockboots, with my Thor-Lo socks only, and put on a pair of XL Jets. They fit. It was tight, yes, but they fit and did indeed go far enough in to be fully useable. Note that I was NOT including the suit's sock in the shoe, which would have made the shoe a tad bigger and may have prevented it from fitting. But I think it's clear that: 1) people with size 9.5 feet should not wear size 9 rockboots, and 2) people with smaller feet than 9.5 may be able to get away with it. I figure the suit's sock adds a half to full size, so people with size 9 and smaller, who are satisfied with the insulation provided by Thor-Lo heavy trekking socks, can probably use size 9 rockboots with XL Jets.
Photos (excuse the crappy cellphone camera):
At first glance it does not appear to fit:
But pushing it in, realizing the shoe material wraps around the foot, perhaps it does fit:
Putting the shoe on, however, and actually wearing it normally, and while yes it is a close fit, it fits:
From the top:
The last part of my test was trying the 10.5 Converse in the XL Jets. I didn't have a drysuit's sock at home to test with, but I doubled the Thor-Lo's, which should be about the same thickness, to simulate it. It fits nicely, except it is pretty tight on the side where the extra bumper rubber is. I think shaving that rubber down slightly would do the trick, as the person mentioned doing with the size 11 Converse to accomplish the same thing. Note that my springs are pretty stretched out, but I think it'll get in tighter once I shave it down a little. And it still gets enough of the foot in the pocket to be considered useable, IMO.
Photos:
Side view:
Top view:
Bottom view:
