Don't know about grass-fed beef, but the taste of grass-fed milk compared to regular is night-and-day to me. I don't often splurge on organic but for milk I do solely for the taste.
I know all about that! Every spring when the dairy cattle in the midwest are turned out into the green fields, the milk tastes of onions. Because wild onions is one of the first things to sprout in the spring!
organic milk mostly tastes different because it's pasteurized at a higher temperature. this makes it last longer and gives it a more of a cooked taste. it's personal preference if it tastes better.
No, I'm not just talking about organic milk. I think there is a huge taste difference even between grass-fed organic milk and "normal" organic milk. (Note I've never seen non-organic grass-fed milk). Normal organic milk doesn't actually taste all that different compared to conventional milk to me.
For me the biggest taste difference is from the grass, not the organic.