I personally would not ever give up my .243. If you compare the same loads from a 6 to the .243 the 6 is gonna show a very slight advantage over the .243. However if you start to use some of the better loads for the .243 like the 90 gr.sirocco in Remington, the advantage is gone. The .243 will have 10 times the available ammo for it and you can find it wherever you go also.
The small caliber packs a helluva punch, I have taken many deer and hogs with it. I have shot big hogs out to 250 yds, with one dead in there tracks shots and have complete pass throughs as well, even at those distances. You have to use the right ammo though, stay away from ballistic tips or core lockts. The core locts are suppose to be improved now with a different bullet but havent found them yet. I prefer 100 gr. hornady's myself. The .243 has been rated by some as the best deer caliber. Lots of people even prefer it for Elk. One other advantage is the gun inherent accuracy and low recoil. The confidence alone makes you a better shot. Put it where you want an squeeze. It'll will be there. I have about a 1 to 2 " grouping at 200 yds with mine. Factory loads too. Nothing done to the gun either. Let us know what you decide.