Water Gardening: Need to enlarge, add 2nd or do something, 4 by Spitzkopf

Spitzkopf wrote:
I have 2 Koi and 2 feather tail gold fish in a 170 gal preformed pond. The Koi are over a foot long and the gold fish are over 6". Their going to have to winter again this year in this pond but come spring I need to do something. Water stays clean and 600GPM pump only runs 10 hrs a day. I recently bought a new sub 3350 GPH pump, sub 10,000 GPH and a jet 2000 GPH (none in use yet). I've also acquired the most of the makings for 2 ea 50 gal bio-filters which I will hide in a hollow rock.

So my dilemma is this:
1) Rip this pond out and put in a 2000 gal with EPDM liner where this one is and add waterfall in from bio-filter.
2) Add a second pond for Koi only (assume they get 20" each = 400 gal min) and leave this one in for gold fish.
3) Make a river flowing into this pond at maybe 4K to 5K GPM and leave all fish there. One problem with that is the wintering.

In the photos below, left to right: Aug 2010, Jun 2011, Oct 2011, Oct 2012 and last is a layout for new 3500+ gal (5' deep) pond with beach but DW frowned.

I'm open to new ideas.