If your frame rates are in hundreds you don't apparently have vertical synchronization (V-sync) enabled. Just so you know, that might cause some tearing issues in the image.
I'd take a deeper look in the settings of the TV to find if there's a "PC" setting somewhere, allowing for 60 Hz. If not, a real monitor of the same type as the two other ones might be a good add-on on your shopping list.
The 380X will definitely be an upgrade. A rule of thumb I heard back in the nineties tells to double the performance level in order to really see any benefit. And getting it from a local dealer makes it so much easier to deal with potential warranty issues.