Goats aren't all that big, so yes, the 243 is enough to bring one down. My concern, though, would be the wind and distance factor. I'd expect the shots to be longer rather than shorter, and in the open plains, the wind can be tough to deal with. A bigger bullet should have fewer problems with wind drift, so I'd go with one of your bigger rounds. There's no such thing as overkill, IMO. If you hit them in the meat, you're going to have meat loss regardless, so I don't even look at that as a factor.

I don't think you'd be 'overgunned' with the 300 wsm. Of the 3 I shot last year, I used a 7 wsm, a 7mm rem mag, and a 30-30.

<------------ The one in my avatar was taken with a 25-06.

As for the meat itself, some will tell you it's not as good as venison, but I don't really feel that way. Just make sure it gets cut up and on ice right away. IMO, a lot of the guys who don't like speed goat have eaten them after they've sat too long in warmer-than-typical-deer-season temps. Plus their hides stink, too. Get those nasty sage&musk-smelling hides off asap.