Frankie Dettori said Moon Ballad's superior speed was the main factor in his decision to partner that colt instead of Grandera in the Dubai World Cup (UAE-I) on March 29.But Dettori admitted he was far from certain that he made the right choice between the Godolphin stablemates. "Grandera looks a million dollars and he could win," the flamboyant Italian said."But you can't count on me -- I might have got it wrong."Marcus Tregoning spoke of the unknown fear factor of Dubai World Cup favorite Nayef tackling dirt for the first time in a race on Saturday.Tregoning was on hand to watch Nayef work under big race jockey Richard Hills at Nad Al Sheba's Breakfast With The Stars event at 8.00 a.m. Dubai time today. The 5-year-old will also work tomorrow morning and again on the day of the race.Nayef look on good terms with himself in a workout with two stable mates, including the high-class Ekraar, a runner in the $2 million Dubai Sheema Classic.His trainer said: "Nayef has been here since November and he looks fantastic and hasn't missed a day's exercise."He's worked well on the surface. A race is a totally different scenario, of course. He has got to face the kickback but a small field (of 11) would be an advantage in that respect and I'd be hopeful he'd be OK. It would be an advantage if they go fast as he would stay on well in the long straight."With Moon Ballad and Frankie Dettori drawn outside of 11, alongside Harlan's Holiday in 10, a strong early pace looks likely as that pair bid for prominent positions. Because of his experience on dirt, Tregoning nominated Harlan's Holiday as the biggest threat, reasoning: "You have got to respect the American horse with his experience of the surface. He's a solid performer on it."