Nate, I just looked through my shots and you're going to be disappointed as they're all with the MKIV and 300 f/2.8L IS +1.4x or 2X, and my 7D shots are with the 70-200mm f/2.8L IS II +1.4X.
I will tell you that you do lose some IQ with the 2X as previously stated, and it does slow down the AF by 75% according to Canon. I would not recommend it for fast action that will zoom by you, like downhill skiing, slalom or boarder-cross as that would be too aggressive for this combination, however your usage sounds like powder skiing from far away with the subject coming towards you, and not zooming by. That's why I'm saying that I think it could handle it.
Do you already own the 70-200mm II? I would definitely recommend the 7D for a backup crop body for sports. The 100-400mm is a possibility too, especially @400mm. Renting both lenses may also be a good idea. I've seen some great shots of the Blue Angles with the 100-400mm from Air Shows, with a low contrast background and it performs admirably.
The Skiing shots I had were with the 1D-MKIV and bare 70-200mm f/2.8L IS II and I didn't have any problem with the low contrast snow because I was able to focus on their ski jacket.
Sorry Nate, as I know that this is not what you're looking for, but all I found were some test shots with the 7D and 70-200mm II and 2X, below.
All with the 7D:
The 1st image is with the bare 70-200mm f/2.8L IS II @200mm f/9
The 2nd image is with 2X @400mm f/9
The 3rd is with 2X @400mm f/5.6
The 4th is with 2X @400mm f/5.6
Thanks, I was also interested in IQ and at f/9 the IQ is pretty good. I didn't expect it to be as good.
Yes I own the 70-200 and I dont want to buy another zoom lens for the moment. I live in Hungary where I dont have a big variety of lens renting.
So I think I stick to a 2nd body.
1DIV is out of my budget but 1DIII is the same price as the 7D...Is the 1D that much better?
The only problem is, that I carry most of the things with me. Usually 3 lenses 2 flashes 1 tripod and some accessories. The reason is that usually I always need the lens that I left home...So the only thing that I dont like is that the 1D weights twice as much as the 7D.