Hey, Orie. I would have to agree that you would probably want to get one from some sort of dealer that would allow a return or a testing period to make sure you don't get one with problems. If you could find one at KEH that would be good. As far as I can tell there isn't a whole lot of difference as far as features go between the F6, F7, and F8; supposedly the more recent models have sturdier innards. If you look at an F6 make sure it has the modern style shutter speeds like 1/15, 1/125, and 1/250th rather than the older 1/10, 1/100, and 1/200, or something like that.
Mine is a F6 that I got used. It worked well for the first 100 rolls or so, and then got all crunchy on a cold winter day. I sent it to a repair place that advertised widelux repair, and they said it would be about $350, but got it back unrepaired about a year later; they said they couldn't get parts because the Panon factory in Japan burned down. Then I sent it to www.camerarepair.com and they fixed it in about 2 weeks for a little more than $200. It works great again.
They have f/2.8 through f/11, and the 3 above mentioned shutter speeds. I've never tried a Noblex, there are several models, but I'd look into them before you buy a Widelux; they probably have more features, and they are still in production which hopefully means any repairs shouldn't be a problem.
I'm trying out a friend's Horizon 202 right now, but I haven't developed any film yet. I'll let you know how it turns out. Just from using it I can say I like the extra shutter speeds (1/2, 1/4, 1/8, 1/60, 1/125, 1/250). The aperture goes up to f/16 on the Horizon 202, but at f/11 on the Widelux everything from about 3' to infinity is in focus anyway. Of course the Widelux looks and feels very nice as it's an all metal camera. The Horizon is covered in plastic, and seems a bit clunkier.
I think the Noblex has focus adjustment; both the Horizon and the Widelux are fixed focus. I think I've read that there is a second of delay between hitting the shutter button and the actual exposure on the Noblex, while it gets it's electric motor up to speed. The Widelux and the Horizon happen pretty much instantly.
A swing lens pano camera is a lot of fun to use.