Doc, what do you plan on using the 6.8 for? As the others mentioned need more info, namely who built that match upper?! I'd say if you have the works, like pinned sights, set front sight, hooded arpeture, fast barrel (is it chrome lined or no?), and goodies to go with the match upper that would command a bit more than the average upper (I shoot national match so that is why I would not want to let mine go obviously). Being a gas piston 6.8 is different but in my opinion unless you have a specific purpose or are a 6.8 fan boy, I would say that your 5.56 match upper should be hard to let go of. Gaijin says it well though, if there is alot of ammo to go with the deal (magazines too?!), then by all means have some fun. NOW, if he said he had a grendel upper mehh, my personal opinion I'd be beating him with a club to hurry up and trade it over, especially if there is even a few rounds to go with it.