I have a 6x45 and would take it over a 223 imp but thats just me, they are very close in drop out to about 400yards and the 6x45 carrys more energy and you can use the 6x45 in some states to hunt deer and its a great round to start a new hunter with. the 6x45 is one of the least picky rounds I have ever loaded, I mean you can load alot of powders and bullets and get great accuracy with almost any combo. I have shot many deer with mine with the 85 partition and havent had one run more than about 30yrds,while I keep my shots under 200yrds I feel it would work fine out more if realy needed but I have bigger and faster stuff for that.
my varmint load
sierra 80grn blitx boatails @ 3025
12.2 drop at 300yrds with 100yrd zero
75grn@ 3000fps (maybe you can get more but this is a what I found online)
11.9@300 2 27.5@400
everybody likes what they like but feel the 6X45 is a better mid range varmint round and can be a great closer in deer round.also to get the 3000fps I have listed for the 223ai you would have to load them very long and lose the use of the magazine in a ar from what I know but I am no expert