After differing but impressive lead-up form, with usually perfect manners and on their home track, it is hard to see how one of the pair won't win. But who could come down to tempo.
If the Cup turns into a heavyweight slugfest, Thefixer would seem the best equipped to handle it, whereas a slower Cup with a winning time between 3m 55s and 4m 00s would seem to play into Spankem's hooves.
"I think it is fair to say Thefixer can do more work in a race but Spankem might be a touch faster," says Purdon, aiming for his fourth Cup in a row.
"I couldn't be happier with them. Spankem has gone well all campaign, while Thefixer has really improved in the last two weeks.
"So it might come down to manners and the runs they get."
If punters assume the pair both step equally, then the problem for Thefixer could be a rival to push the pace, with Victorian visitor San Carlo looking the most likely to turn this into a sub 3m 55s Cup but his ace draw is a worry.
Thefixer overcame a mid-campaign setback to win the Cup last year and might deserve to be closer in the market to his stablemate but Spankem has so few weaknesses and looks in the zone, so he is still the one to beat.
Purdon doesn't have the usual domination of all markets today but suggests, in order, Amazing Dream (race eight), Taxman (race 12) and One Change (race seven) are his next best winning hopes after his Cup quartet.
And while he believes Ultimate Sniper is working well enough to take the junior free-for-all, he admits to favouring northern Triple Eight after his booming Kaikoura Cup third.
