Everything Apple (the Mac heads thread)

This should explain the processor differences
http://www.trustedreviews.com/opinions/b­est-intel-processor-core-i3-i5-i7
@Dammit

The mobile processors' branding doesn't reflect the chips' speed well though.
Looks like, from https://en.wikipedia.org/wiki/MacBook_(Retina)
that the 3 chips are

Core m3: m3-7Y32
Core i5: i5-7Y54
Core i7: i7-7Y75

Side by side
https://ark.intel.com/compare/97538,95452,95441

There's almost no difference apart from the clock speeds. The i7 has a few things enabled the other two don't. Most you won't care about

Intel® vPro Technology
Intel® Stable Image Platform Program (Intel® SIPP)
Intel® Trusted Execution Technology
^ ^^ ^^^ for enterprise management/security I think

Intel® TSX-NI
^ looks like something that helps multi-threaded applications. But it's only a 2 core machine so probably not massively helpful (maybe, I don't know really)

They all have the same number of cores, the differences are just clock speed (1.2, 1.3, 1.4 GHz) and graphics chip speed (900, 950, 1050 MHz).
So looks like the core i5 version will be approx 8% quicker than the core m3.
And the i7 will be ~9% quicker than the i5, and 17% faster than the m3.

Probably a bit less noticeable for anything where the processor isn't maxed out though.

So they're all fine. Pay more, get faster but nothing huge.