Are you gold or platinum elite? I only ask because the agents there tend to be more knowledgeable about international award travel. I suspect that's the really problem here.

I went to Continental.com and was right away able to identify standard FF seat availability for Y and J on the GUM --> CNS route for departure of 8/12 and return of 8/20. I am going to Melbourne in 2 weeks and originally had checked into the Cairns routing and there was plenty of availability.

I'm not sure where you are departing from, but I did a thorough analysis and even though you fly more miles on MH, it's quicker than on CO because inevitably the routings I found had me spending an overnight in Guam.

I would try calling again, or going to Continental.com and using their award search engine to find dates that are available. And of course I would actually add up in the inflight and onground transit time for both CO and MH, just to make sure CO is quicker. For me the routing was going to be MSN-->DTW-->NRT-->GUM-->CNS-->MEL with an overnight in GUM and the MSN-->EWR-->KUL-->MEL route had 2 less airports and about 10 less hours of transit time, even though I did indeed spend more time in the air , but I still got their sooner.