I hope you're planning a 180 or 230 for the Sailfin!
What was nitrate at while skimmer was running? I think if you're getting nitrate creep that bad already that you should try to look for a used skimmer to put on the tank. Could you put a hang-on skimmer on the side or back of the tank (instead of in-sump)? If so, try to find a Deltec hang-on skimmer since they hold their price well (they are excellent skimmers) and will be easy to re-sell when you have the big tank set up.
I tried Googling to see what you're dealing with, and I can't find any pictures of the sump. Could you post a link maybe? Or at least the dimensions of the skimmer chamber? SWC Cone skimmers have a really small footprint because of their internal pump, and they are reasonably priced.