Umm, Did a test a month ago or so. I know for a fact that they go atleast 10+k.
I fired one at a 2K base from 12K up straight down, I dived and followed it as close as I could, I saw it hit when I was a few thousand AGL.
But yeah, I do wish there was a bigger blast radius. If you see some real WWII footage (which I saw today) the rockets on the IL2 could take out numerous tanks in one pass with 6 rockets. Right now, they have a blast radius of about 25ft? and don't even do much damage. Same goes for bombs.