Agreed, at least, for the 8950....defintely stick to dual channel vs quad. The documentation states that the speed gets reduced down to 3600mhz if you go quad channel (which is dumb imho). With the lack of performance between dual and quad channel, unlike dual vs single, I would defintely want to stick to dual channel and keep the speed at 4400mhz vs dropping all the way down to 3600. 32gb (2x16) at 4400 would far outweigh 32gb (4x8) at 3600, IMHO. FWIW, im in the process of rebuilding my 8950 with a new Mobo/psu/case and ram because i needed to boost my 32gb ram to 64 or 128 for my photography and photoshop workflows. In discovering the performance loss when going to quad channel on the 8950 I decided to go 64gb (2x32) and, while i knew about the MHz cap, discovered that the latency is also capped. Which pushed me towards a rebuild. Anywho, yesterday my parts came in and I went ahead and ran some tests with GSkill Ripjaws S5 64gb (2x32) 6000mhz CL32 and, per PassMark memory mark testing, there is a slight boost in performance with the Gskill ram in motherboard marked slots 3 and 4 vs 1 and 2. In another post on here i uploaded a bunch of screenshots illustrating this. I think its weird that theres better performance in slot 3 and 4 vs 1 and 2, which CPU-Z sees slot 3 and 4 as Slot 1 and 3 while slot 1 and 2 is shown as slot 2 and 4. Not sure about that one. But anywho, the default 32gb sticks had a memory mark score of 3220 or 76% percentile while the Ripjaws in slot 3/4 had a score of 3310 or 80th percentile.
As the Subject says, I'm trying to decide if I should buy a desktop XPS 8950 (or 8960) with one 16GB DIMM or 2 x 8GB DIMMs. For now, 16GB of RAM is all I really need, but I want to leave myself with the flexibility to add RAM in the future. Here's what I'm thinking about: 1- (This may be outdated information, but) I'm used to reading that RAM should be installed in pairs. If that's still true, why would Dell offer a computer with only 1 DIMM; and why might I choose one DIMM over 2 DIMMs? 2- Let's say I choose 2 x 8GB DIMMs for now. If I want to increase to 32GB in the future,  I can do that in two ways: I can add another 2 x 8GB DIMMs or I could replace the existing 2 x 8GB DIMMs with 2 x 16GB DIMMs. If I add an additional 2 DIMMs then all four memory slots will be filled, but I read in another post that when all four slots are filled, the DIMMs will run at 3600MHz instead of 4400MHz. Is this a fact? As always, thanks for your help.
XPS 8950, installing one 16GB DIMM vs two x 8GB DIMMs