The David Bourke is a heat of the VRC-CRV Winter Championship which has a final over 1600m at Flemington on July 5.
One recent blip on Regal Zeus' radar was his fifth placed finish to Pride Of Jenni in the Listed Anniversary Vase (1600m) at Caulfield on May 3, three runs back.
"He controls the speed in most races, but against a horse the calibre of her he couldn't," McArdle said.
"Whilst the plan of attack was to come back and sit off her, he didn't want to do that, and he just raced out of his comfort zone.
"He still ran fifth and was a bit soft late, but he did all the chasing, and he's bounced back, both at Flemington and at Caulfield last start."
At his most recent start, Jimmy The Bear, an opponent on Saturday, had the better of Regal Zeus, and McArdle said if not for wanting to run down to the fence, the result may have been different.
"He had the pull in the weights on us that day," McArdle said.
"But it's interesting, Harry (Coffey) thought if the rail had of been on, that might have been the difference in the margin.
"He handles give in the ground, but he's better on top of it, so hopefully the rain will stay away."