[sneak]

I did this only because Apple didn't sell the 4-slot 27" iMac populaed with 4x8GB (32GB) - max BTO was 4x4GB so I got 2x2GB and threw them away and put in 32GB.

Other than that, the Apple ram is not so expensive that it's worth dicking around with making sure you have compatible speeds/pins/size imho (unless you are going Mac Pro in which case the difference on, say, 64GB or more would really add up).

Basically I just don't worry about stuff that amortizes out to under $500-1000/year. (e.g. an iMac for me has about a 36-month useful lifespan)