I have a 10.5 in 6x45 and I can get 2450-75 or so with 87’s. Also just over 2500 with some 85 soft points I got from grafs in bulk. It’s a great SBR round really. When I was working at AO, We cut it with a “6x45 Wylde” reamer, and used a brux barrel, it’s also very accurate, for what it is. Especially so with Sierra 70 gr match kings. I have another barrel we made I’ll be listing soon that’s around 14in or so.
Craziest load I have is some of the Lehigh defense 57 grain cqc with the aluminum tip removed, and AA1680. I ordered them just for this, and they came with no tips, which was serendipitous as they won’t fit the mag with the tip. They are crazy fast with the 1680. Think along the lines of a 16 in 223 with 55’s.
Also note if you have a KAC NT4, it can handle 6mm, just have to bore out the adapter. I used a griffin armament comp.. super loud but actually works pretty well, and suppressed it’s not bad at all.