I voted for 300 as well, but I beleive 300-400 is very doable by most three gun shooters.
I also know that having a place to practice the longer distances comes into play, as most people do not ( I do).
I agree with Trapr and Kelly that the top shooters will clear a 100-350 or so yard stage much faster than other competitors and that is what will seperate them on the score board. A time out really frustrates competitors.
I like shooting the carbine from point blank run&gun and out to 600. Anything in between is ok as well.
Finally, It is up to the MD of the matches and I will run what I brung on whatever they have setup. If I personally do not care for it, then I will not attend again.