For most of his career, Strait Acer has been like an active toddler – high energy, headstrong and a little wild.

Even when he strung together a trio of wins during the late winter and spring, then was highly competitive in the Silver Eagle and Golden Eagle, trainer Ed Cummings said the horse was still immature and burning energy at the wrong times.

It wasn't until a trip to Melbourne for the Group 1 Sir Rupert Clarke Stakes (1400m) that Cummings finally saw a mental shift in the son of Headwater.

"I don't know that the penny dropped at any point until his run in the Rupert Clarke," Cummings said.

"He's always been a rambunctious horse, that seems to be a personality trait that follows the breed.

"But he was definitely at his most professional while he was in Melbourne.

"I'm hopeful that has helped bring him on and makes him become more professional so he saves all his energy for when the barriers open."

Cummings hopes that a more mature attitude is replicated on Saturday when Strait Acer resumes in the Group 2 Expressway Stakes (1200m) at Randwick, taking on a select field that includes dual Group 1 placegetter Buenos Noches, fresh specialist King Of Sparta, and speedy pair Malkovich and Coal Crusher.

He is particularly interested to see how the four-year-old copes with 1200 metres, the shortest journey he has raced over, and says Strait Acer's performance will go a long way towards dictating future plans.

"It's an opportunity to see how he can compete in a high-class race over 1200," Cummings said.

"If he was to perform very well, it opens up more options for him.

"He has thrown himself up as a quality 1400-metre horse, we're just trying to work out whether he is going to be as effective at 1200 and/or 1600."

Having accelerated his career from provincial to Group 1 level in a single preparation, just where Strait Acer's ceiling lays also holds some mystery.

Cummings, however, is certain of one thing - the horse's best is still ahead.

"I think the horse is on the way to the peak of his powers," he said.

"But no one is clear what that peak might be at this stage."

Tommy Berry has been doing the preparatory work with Strait Acer and has the race day ride, while apprentice Zac Lloyd links with stablemate Long Genes in the final event.

The latter returns to racing as a gelding after showing glimmers of promise at his initial campaign, including a midfield effort in the Gloaming Stakes when finishing less than two lengths from the winner.

Cummings will be happy to see Long Genes doing his best work late first-up as he keeps an open mind on plans.

"He's eligible for easier, so we're giving him an opportunity to run well in easier company and we'll see where it takes him," Cummings said.