It's kind of new to me also but from what I gather it can be a real barrel burner if you load it to the max. I'm just shooting the 69 grain SMK at 3365 fps with 41 grs. of 4831.
Everyone says load it on up and get the most out of it! I always go for the most accuracy rather than the most fps. The main thing about this rifle is the 1 in 8" twist allowing the use of heavier bullets for real long range advantage.
I'm thinking I'll probably settle on the 77 grain SMK for most of my shooting! I'm still in the try and see mode right now.