if there is ANY way to increase two of those drain lines I would do that.
I'm running about 1100gph but my drains can handle over 2000gph
1" drains can get clogged so easy.. I had to tear my plumbing apart twice when I had my plywood tank because the drains got clogged
go to 1.5" on the two outside drains and leave the third for emergency
I have horizontal runs in my plumbing and it does not reduce the efficiency of the drains