The width is going to be the issue with CC, that is why everyone likes the single stacks. A car/travel pistol is a completely different set of criteria.
I don't know why Springfield calls their double stack small one a "subcompact" because in my mind, they're still just "compacts", which are usually smaller versions of full-sized double-stacks. To me, a subcompact is a small single-stack handgun, like the XDs, which is MUCH smaller and THINNER than the XD "subcompact."
So, on to the other part of this - I completely agree that "car gun" and "CC gun" are different. LSUBrad, if you haven't watched my First Time Buyers video, I suggest you do. Even if you have bought some in the past, it's good to get a refresher on the sizes and such. First Time Buyers
Personally, I think the best middle ground for a handgun that must fit both roles of a "Car gun" and a "CC gun," a compact is the way to go. It has the ability to accept full sized mags but also retains a small profile with the smaller mags. My Ruger SR9c is perfect for this, although my Kahr CM9 is in the car most of the time.
If you want it to be a dedicated concealed gun, go single stack and you won't regret it. You can incorporate your larger guns into your carry rotation later on but your smaller gun will get carried more often. Start there and then slowly move to the bigger handguns.