Kamui is his only chance, and it's a pretty good one. Sasuke is fast, but Kaksashi is no slouch himself either.
Plus the whole "Sasuke's speed w/o susanoo" thing really doesn't work for two reasons:
1. We've seen Kakashi use Kamui on fast moving targets before (Susanoo arrow, Naruto, Lightning kunai, nail, rocket). The Susanoo arrow is particularly impressive, because it was coming right at him from close range, which means Sasuke would have to be careful how he tries to blitz Kakashi
2. It's really not important whether or not Kakashi catches all of Sasuke with Kamui. Kakashi's kamui is unique as it's been shown on two separate occasions that even if he can't get your entire body, whatever body part he does manage to catch will get ripped off. Both Diedara and the Gedo can attest to that fact. Last thing Sasuke would need is to have his arm ripped off.
But it's no guarentee. Basically with Kamui Kakashi has a debatable chance. Without it he has zero. So I wouldn't say he wrecks current Kakashi, but he's better than him regardless