While they don't have your specific pump to choose from you could pick a similar one and play around with this head loss calculator to see roughly how much flow you will lose by going with smaller diameter plumbing.
http://www.reefcentral.com/index.php...oss-calculator
In my opinion it would be a waste of money/electricity to use small plumbing with a large pump. My 120gal and now 225gal have used a Reeflo Dart with 1.5" plumbing for the return line. You could run 1.5" as your return and then T it into two 1" lines for the bulkheads.