I'm going to lean to the X2.2 over the Chameleon only because a lot of people are very happy with the X2.2s and I haven't read much on the Chameleons.
Theres two ways to go solderless with the X2.2. One way is to buy an X2.2 and a solder add-on or buy a X2.2
plus. As for the Chameleon I'm not sure about, but I think it needs to have an add-on.
As for limitations on these chips, there really isn't one I can think of right now. Maybe a little while down the road…
As for finding out your XBox's version there isn't any 100% positive way other than to open it up. But this should worry you b/c you're going to have to open it up to install the modchip any way.
Any here is the link to a guide on how to upgrade the HDD. It will give you a lot of other info as well.
The Ultimate XBox Newbie Guide
And yes you can use the old XBox HDD in a PC but it has to be unlocked first. I would strongly suggest you not do that. If any thing happens to your upgraded HDD you are more or less
SOL.