If you don’t notice any compression artifacts (“blocky” areas of the picture) in the AVCHD, then the MKV won’t really offer you much benefit. It depends on how readily you notice compression in general, the size of the TV/monitor you’re watching it on, and how close you sit to it.
Basically, if you don’t notice any difference between the “original” and “compressed” sides of this picture, then the AVCHD is probably plenty high quality for you. If you can tell the difference, then you’ll probably notice a quality bump with the MKV.
