The furthest north that I know about is East Texas (near Shreveport, LA). About 20 years ago we dug up our first tree from the property and brought it to Hammond Louisiana. It grew very well in the ground and when we know we where moving to Central Texas we started planting seeds. We left the tree behind in Louisiana and moved with us 30 that where about 2' tall in 5 gallon buckets and they are doing great. This spring we had about 15 come up in a large flower pot (thanks to a squirrel) and they all have red leaves and look like all the others. We have never grafted a tree before and as you can see from the picture they all look red.
Kyle I would be glad to send some to you to try if you want them. What do we have to lose?
Thanks for chiming in.