Hang on, copy and paste is definitely not my recommended technique. Never C/P, only Place.
Blend If can be awesome, but it's not infallible. Make sure you always check its results VERY carefully. I suggest putting a bright red layer behind your Blend-If-ed layer to help examining for flaws.
Well, I'm pretty sure if I was doing it I'd want to do the one-image-at-a-time method. My computer is no slouch, but it definitely doesn't have enough power to be placing an overabundance of full-res images at once.
But it's up to you.