Yep, that is why I went with the 16 Gb memory. My experience with Apple computers when bought new is that the first memory upgrade is price competitive but maxed memory is not. I am sure there are exceptions. Plus I hate wasting my drinking time having to sell shit.
I am currently running my former 16Gb iMac with an additional 16Gb of Crucial Ram. It works the same as before the upgrade, well except for the fact that my R code runs faster. It is the latest non retina version with an i7 and the NVIDIA 775M.
Replaced the nonfunctional HD in our 20" imac with an SSD. Now installing the OS, just happy there were no parts left over after I put it all back together.
You're getting the 27" correct? In that case I would go with the 16Gb as two 8gb sticks. Then when you go to 32gb (because you know you will) you just need to get two more 8Gb sticks. I would also go with the i7 because Head-Case.