Golden Horn's toughest examination yet takes place in Saturday's King George VI and Queen Elizabeth Stakes at Ascot. Can he cope with significantly rain-softened ground? Can he back up for his fifth outing this season only three weeks after the Coral-Eclipse?
Most pertinent of all, can he deliver again against older opposition over a mile and a half, which is surely the upper limit to his distance capabilities?
But the ground remains the most pressing issue. On Friday, the Ascot going was changed from 'good to soft' to 'soft' following a deluge during racing, and more rain is forecast until 4am on Saturday.
John Gosden will walk the course before racing and decide whether Golden Horn takes his chance.
Golden Horn is an unbeaten Derby winner, and his connections, to their great credit, are giving those assessing the current Classic generation ample opportunity to provide an accurate rating. But, unlikely as it may seem, there are more questions to be answered.
Gosden has helped greatly in restoring the status of the King George by running three-year-olds in the race again with some regularity.
Both his winners, Nathaniel and Taghrooda, were from the Classic generation. For the previous decade, owners and trainers of the top three-year-olds seemed to have shunned the feature despite the prestige and money offered.
Golden Horn is the only three-year-old in the field this year, and it is certain to be argued that getting 9lb and more from the older horses is too much. But, in this case, is it?
This is a truly fascinating race. Tactics will play a major part, and Frankie Dettori may not want to dictate in front on Golden Horn as he did in the Eclipse at Sandown.
Gosden also saddles the second favourite Eagle Top, who comes here off the back of a second in the Hardwicke Stakes at the Royal meeting, as well as Godolphin's Romsdal, who will have William Buick again in the saddle.
One suspects that Romsdal has been looking for some ease in the ground, which he is likely to get for the first time (on turf) this season. His third to Arab Spring on 'good to firm' at Newbury in April was very good, while his fourth to Snow Sky in the Yorkshire Cup in May was below his best, most probably because of the quick ground.
Romsdal has always been regarded as a classy recruit for Team Godolphin. He finished third to Australia in the 2014 Derby and second to Kingston Hill in the St Leger at Doncaster later that season. He has given every indication that he retains his ability, and track conditions should bring him right into contention.
Flintshire has been a very reliable Group One horse internationally, Snow Sky is on the upward climb though he can hardly expect to find it as easy tactically as when he won the Hardwicke, while Postponed has form that suggests he could be placed.
Italian champion Dylan Mouth comes to his biggest challenge with a fine record of nine wins from 10 starts. Clearly, he is an exceptional talent and this is his chance to show just how exceptional that talent truly is.
The horse I expect to be the biggest improver is the David Simcock-trained The Corsican, who caught the eye finishing fast on the outside for fourth behind Free Eagle in the Prince Of Wales's Stakes at Royal Ascot. He is set to run a big race.