The Riccarton trainer has a path plotted towards the Group III New Zealand Cup for the 7-year-old which takes another step at Ashburton on Saturday.
Carston holds two strong cards in a rating 75 over 1600m with Edensong joining Sadlers Rock in the first of the day.
Sadlers Rock was heading for the cup last season, when trained by Lisa Latta, but several minor issues plagued his preparation and the cup start failed to materialise.
Carston described Sadlers Rock's fresh up run for fifth behind Diamond Edge over 1400m at Ashburton on August 28 as much better than expected and it has him feeling positive heading into cup week.
"The 1600m is not his specialty but you have to get the miles under his belt and I'm really happy with him," Carston said.
He said it was hard to know what would play out in the small field but he was taking confidence in having one of the best judges of speed around in David Walsh on board.
Sadlers Rock has not tasted victory since winning a premier rating 85 over 2200m at Trentham back in March 2014 but has been in some quality fields and Carston said he would be disapointed if he was not in the top four on Saturday.
The top weight at Ashburton, Sadlers Rock will carry 59kg but Carston said Edensong could be the better chance of the two.
He is expecting improvement from the mare after she ran fourth in the same race as Sadlers Rock's on August 28.
Classy mare Madam Victoria, who is nominated for the Group II Couplands Bakeries Mile, is a $2.10 favourite with TAB bookmakers to win the open handicap over 1400m at Ashburton.
In two runs back this campaign, Madam Victoria has a second,over 1200m at Riccarton and more recently a third over 1600m at Ashburton on August 28 but Carston is hoping he can spoil the party with Tacticall who is a $6.50 chance with the bookies.
Carston said Tacticall is in great shape but his only concern is her poor record at Ashburton.