Not for me,but guessing . . . - - -> bullet speed/trajectory,a little less recoil,something different,possibly more.
Will default to the OP.
Your questions above are certainly valid Wes. I thought about building a 204 about a year ago but decided not for me.
Calling yotes or over bait at <300yds for a somewhat quicker follow up shot or possibly not quite as much holdover (??).
Thru some bookwork I found out that with a "longer than" 16" bbl gun (20-24"),and shooting a 40gr,the 223/5.56 is pretty close to the 204.
I killed whole bunches of yotes in Maine with my 24" 223Rem/AR shooting the 40gr NosBalTip. Shot damn flat . . . and would not be pushed around by the wind as much either. --- SAWMAN
ADDED: Back then there were a couple 35gr bullets on the market which I tried,but they were not enough faster for much trajectory advantage,and were not as accurate.