"She is just awesome. She's so strong and kind and really wants to work with you. She has great stamina, but last start when she got unbalanced on the bend and I had to ask her, she actually showed good speed.
"So she has more speed than people realise, so we have options today. But she will be rolling forward from barrier eight and be handy."
As strong as Self Obsession is, her stablemate The Perfect Pink comes out of stronger form races but goes into today with some doubts over her 2400m credentials, although that could be said for most in the race.
If she can settle and swoop, she could beat the stablemate for speed in a race with plenty of other fillies who can run well.
Imperatriz is the hare to Self Obsession's tortoise, albeit in a different race, the 1600m of the Levin Classic which has found the right date in the racing calendar judging by the depth of today's field.
"She's so different from the other filly," says McNab. "She's more sassy and all energy and just so fast. When you let her go, you have to hold on."
Imperatriz was dazzling winning in easier company last start and meets some serious boys in the classic, with On The Bubbles, Shamus, I Wish I Win and Mohawk Brave all capable of winning, their chances may be decided by the tempo.
If there is genuine tempo, the 1600m around a big track like Trentham can be testing and might be right at the end of Imperatriz and On The Bubble's stamina range, whereas Shamus looks like a horse who would enjoy surging late.
"I have options there, too," says McNab. "If we go slow, then she can be up on the speed, but if they really roll along, then I can let her settle a few pairs back and hit the line hard."
McNab could start the day with a juvenile win on Slipper Island, who only narrowly went down to subsequent Group 1 Sistema Stakes winner Lickety Split on debut at Ellerslie.
A big day today could put him 10 clear on the premiership.
"If I keep riding well and stay healthy, then I'll have a shot but Craig will be tough and Lisa [Allpress] never gives up, so there's a long way to go."