These will test sync alright. Very, very few people can (from what I have heard) do these really well fast and in sync like Yngwie does. I have been working on a descending circular 4 lick for almost a year - and the sync is one of the hardest parts to it. And it also depends on if you are alternate picking it all. If you use escape notes (pull offs) in combo it makes it a lot easier on the string changes. If you want to alternate pick it all it is pretty hard.
I have done a LOT of slow and fast practice to get it to happen. Very considered and focused. By it takes a lot of work - at least has for me lol