I build high end systems, quite a few of them, and I work with them all the time - you can read all the reviews and BM you want...sorry, but it doesn't relate to real world performance gains that are possible...BMs on nothing more than an entry level figure - they do one thing, period, run the software that was programmed in. Reviews can be and often are worse, especially if you really READ them, you often find things said that make no sense and are utterly wrong - i.e. I seen a these 'Expert' writers often say 'The DRAM DIMMS didn't load the proper timings under XMP from the SPD' as if they thing the sticks them selves go in and program the computer...wrong! what's on the SPD is nothing more than info. It's up to the BIOS to take that info and implement it as close as it can in the system - now then that can be real hard to do when say you have a set of stick that conform to XMP and need a tRFC of 278 or of 314 and the BIOS itself has a limit of 255 in it - yet they advertise they can run these things - Memory updates make up the bulk of most all BIOS updates and are the ones you don't hear about. Another good one is people reviewing DRAM (and this is my favorite but there's plenty similar) a reviewer (who claims to be a memory expert) did a review on a 16GB set of DRAM and claimed to have run it under XMP, and talked about low performance....Hmm, looking at the review, that 16GB 'set' was actually half of a 32GB set , the label was shown in one of the pictures, he tried it on an old BIOS that didn't support the config (and obviously could do it manually), so he dropped to 16GB and enabled XMP which can work and will run, the problem with performance - the 8 sticks set (8x4GB) is the basis for the XMP timings, and require a tRFC about 100 higher than would a 4x4GB set...so he was running the 16GB at a tRFC 100 higher than it should be...so of course performance lagged...there's tons of these out there.
What I like to do is set up identical systems, or use a single system and simply have people sit and do stheir thing on say a system running 1600 and again on one running 2133 or better, (and not just email or a browsing session), I want them to multi-task, open numerous apps, use large data sets, have a virus check in the background, etc. You have them do this blind, meaning not knowing what DRAM they are running - about 85% always pick/want the rig with the faster DRAM and comment that it's much faster, what did you do.
As far as costs, that's another thing that I look at both for me and for clients IS IT IN THE BUDGET? DO YOU NEED IT? for me yes, I am often using 20+ GB of DRAM between apps, a RAMDisk, VMs, photos, video, GIS, etc at a single session
So no offense please don't tell me that 'current gen intel chips' don't show benefits, the do, as did the third gen, IB, as did the 2nd gen SB and even back to socket 775. And further AMD Piledriver is at the same level of DullDozer the 8150, in general limited to 1 DIMM PER CHANNEL AT 1866, their own words, that I finally got them to admit and have kept the emails as proof. What truly stands out in DRAM use gains is AMD, yes, but definately not the Piledriver, it's their APUs that love fast DRAM for their GPUs