I've been shooting the whisper for about a year now, in fact, mine is for sale in the classifieds. I'm moving to an AR15 in 300 AAC Blackout, which is essentially the same. It's been fun in a bolt action, and quiet with the suppressor. In fact, it's pretty quiet without the suppressor, compared to full power rounds. The 300 BLK gets my vote, because it is the 300 whisper in standardized form. This means you will be able to get a larger variety of dies and brass for it. You can also still make brass from .223. I headspaced mine using pre-formed brass that I bought from a guy who processes it from surplus 5.56. I think you will really like the 300 whisper/BLK/fireball.