In the Middlesex league we have conceded over three hundred a few times, 340 last season(in 50 overs) but we are playing in a tough division(1) and most have overseas players .
Personally my highest score in league cricket is 128 not out but that was when I was good a long long time ago.
In any match I can't remember the highest actual total we have conceded but we did play against a touring Zim side in a 50 over game Alistair Campbell and either Grant or Andy Flower scored big unbeaten tons.
And this was chanceless batting, absolutely everything was one the deck unless it was clean over the boundary
I remember it well because a few of us in our 20's thought we were pretty good....and then realised the gulf with the pros was.....well.....absolutely huge.