Memory under 'About this Mac' is reported as '32GB of 1333 Mhz DDR3.' Therefore, not reported as its native 1600 Mhz. Was able to install four (4) mixed serial 8GB SO-DIMMs of Samsung PC3-12800 (1600Mhz) DDR3 SDRAM memory modules (Samsung Memory sticker IDs listed as M471B1G73DB0-YK0 1338 and M471B1G73CB0-CK0 1251) in a Mid-2010 27' iMac with an Intel 2.93Ghz i7-870 processor. 'PC3-12800' is the name used in the memory industry - 12800 indicates a peak transfer rate of 12800 MB/s (of course, the actual performance in your case would be brought down to 8533 MB/s, matching PC3-8500).'1600' is the data transfer rate per second specified in millions (the technical term is 'clock frequency') - '1600' here means it supports up to 1600 million transfers per second - in your case, it will be slowed down to 1066 million transfers per second since that's what your Mac is designed for.'DDR3' is the type (and must be the same as what your computer has).However, your system will operate at the speed of the slowest memory module. Memory is designed to be backward-compatible, so generally speaking, you can safely add faster memory to a computer that was designed to run slower memory.

Here's some relevant information from Crucial on memory speeds (emphasis mine):

You could add the 1600 MHz memory for your MacBook Pro even though it's designed for a slower memory (1066 MHz) - it ought to work, but you'd be better off buying from a place that accepts returns.

Mac pro 2007 16gb ram