Grain finished meat is pretty gross compared to wild, but sometimes thats all you can get your hands on, and its not going to kill you to eat it, but its not that great.. Since your food is supposed to be making you healthy, since your food isnt healthy, its not going to work right. I found the fat more gross than the meat on grain finished animals. The main reason that i dont like store bought meat is that it always smells like hand sanitizer to me and that really puts me off my food haha.
But right now im getting beef from my local butcher who is butchering their own cows that they're only feeding hay and barley as the grain to.. It is a huge difference over something that is fed corn and/or soy as well. This stuff is pretty good and almost up there with a grassfed meat in my opinion. So yes, i think what something eats is important and does make a difference, so you just get the best that you can, sometimes its not grassfed.