with a quad core prozessor unit (i7 intell) - there a maximum 800% available.
4 cores - each virtual double used (or so).
I only brows thru a file ... scroll down ... at thumbnail view ... and seconds later ... cpu is very busy.
When i'll render new previews .. i think it's okay ... but not at simple picture viewing.
On my iMac ( 16GB, 256 SSD, i7 ) there was no problem such this.
i transferred the catalog from my imac to the macbook ...