In terms of speed, both are elites. Itachi countered Sages and Jinchūriki (that trounced Raikages) while Kakashi matched gated Gai and exchanged blows with cloaked Dōjutsu Jinchūriki.
However, when observing their shunshin usage, I do believe Itachi has the edge, because his shunshin was shown to be immensely impressive with or without being combined with clone creation.
For skirmishes, they are equal in hand-to-hand, but Itachi uses weapons to evoke Hachibi transformations, pierce multiple Rinnegan, and force even Sasuke to use a 'quickdraw-kuchiyose.'
Consequently, Kakashi will be outclassed in the opening skirmish, as Itachi's superhuman speed, particular to his hands, should dominate the warm ups. The battle thus progresses to ninjutsu.
At this point, Itachi retains some advantages in key areas. The first being that Itachi has the more efficient bunshin, which further compounds his advantage for Sharingan and style efficiency.
And while both Itachi and Kakashi can splurge on Raiton or Daibakuha Kage Bunshin, the presence of efficient yet powerful Karasu Bunshin awards Itachi an attritional advantage in caution.
Moreover, while Kakashi does have the nifty ability to combine bunshin with doton assaults, it should be noted that Itachi's Karasu Bunshin permitted him the same "drop" on Sasuke and Kabuto.
As for pew-pew offense, katons are much better in this match, because they are indeed lethal to non-cloaked, non-regenerating shinobi while also possessing a sizable area of effect.
The widespread dominance of raitons is only present against durable ninja... which Kakashi is not. The speed feats of Itachi's jutsu was further amplified in his Sage and Jinchūriki feats to boot.
This is likely a throwback to Itachi's sealing speed, as he can create jutsu "superhumanly" as Kurenai puts it, and allows him to preempt Sharingan precognition itself and arguably Sage senses.
As for intelligence, Itachi was never fairly outmaneuvered. In the instances reported, he was not only outnumbered, but was weakened or holding back according to his opponents.
The portrayal of Itachi, at this point, paints him as smarter. He figured out how to defeat Edo Tensei, countered Rinnegan tricks, and was praised as superhumanly perceptive above all Uchiha.
And then there's genjutsu. We've seen C's genjutsu be effective for openings. While the window was small, it was present, and Sasuke needed only a small window to defeat Danzō.
This may be why Kakashi learned to avoid Itachi's eyes, as he did against the clone, was most likely to avoid these small windows that could lead to Itachi's decisive victory.
However, Itachi still has the small trump card of his Sharingan crow to catch Kakashi in genjutsu, as he did against Naruto, and this could potentially give him the opening for victory in itself.
And then there's Izanami, which can put Kakashi into a short genjutsu by having him kill two Karasu Bunshin in a similar fashion, which is possible without his knowledge. Itachi gets his window.
Ultimately, we can rely on outdated feats to aid Kakashi's case, but that's not necessarily fair, because Itachi was always stated to be held back in some fashion. We ought to use the best.
And when viewing their best, Kakashi is not, and will never be, portrayed as an equal to Itachi in shinobi skill and insight. Kakashi lacks the "Itachi battle factor" that some confuse for "Gary Stu."
Itachi solos. Forever and always.
