Just to chime in for comparison sakes:
I am using ASIO Guard and my performance meter is really quite healthy and low.
I have had that meter creep up into the red though, so I can relate.
It also happened once recently, only because I introduced a 32 bit plugin into a current project.
Then after a restart of Cubse it went away.
I have also had it in the past a few times - but it never seemed to last.
It may take some tweaking to get your system to ‘play nice’. As mentioned there are a lot of different systems and configurations out there.
I’ve noticed that Cubase can be a bit finicky, but for me [specs below] both 7.5.4 and 8.0.30 are really stable with low performance/CPU usage even with half a dozen instances of Kontakt 4 and 5, other VST instruments, some 50 tracks both MIDI and Audio and numerous effects - all processing live without anything bounced. 3 of those K5 's are quite intensive as well - Kirk Hunter’s Solo Strings.
Something that helped was to right click on the Cubase shortcut icon in the quick launch, and in ‘Properties’ uncheck ‘Run In compatibility with Windows 7’ [in my case].
One other thing I can suggest you try is the ‘Audio Power Settings’ given free by a member named Motoko on the Presonus forums.
I’ve been running that for a while now with no issues [other than that 32 bit plug].
I can give it to you to try if you PM me for it.
Additionally, I helped out another guy who was all ready to give up because he was at his wits end.
I gave him a copy of my 7.5 Preferences and he was up and running with that since then and still is.
That was about 6 months ago. I can give you that file for 8 Pro to try as well if you like.