A calibre generated cover will start off at a specific size (590 x 750 I believe), but if any conversions have been done that will have been resized. If you are thinking of using the QC size check bear in mind that will also only work if you have "extracted" the cover image from inside the book (i.e. there is a cover.jpg in the book directory).
"Wading through" is the only realistic way. You might find the "Temp marker" plugin with a keyboard shortcut assigned useful for that.