not true, more ram is always helpful with video editing. fcpx is sometimes happy to use 20 of my 32gb ram. and don't get me started on after effects' ram preview. i'd advise for the 16gb AND the i7 quad core, if it's a laptop.
so, the base 15" model, with the best processor you can afford, as you can't upgrade any of it later. a discrete gpu can also bring render times down.
the best "bang for the buck" would be the retina imac with the fastest processor you can afford. you could upgrade ram with cheaper (but still as good) third party ram later, as ram in the retina imac is user replaceable. (e.g. $300 for a 32gb kit from owc)
having said that, a 13" mbp should already be enough for editing gopro videos, but everything faster makes it, well, faster.