EDITED.
In 2005, i built a system with a 7800 gpu sporting 256MB of GDDR3. Today, i'm looking to build a new gaming rig. I've kept up with CPUs/GPUs/SSDs/RAM but little else.
My budget is 2K for a tower
Inside is Fury X or 980ti GPU, 1TB m.2 SSD, i7 skylake and I dunno about the rest of the components,
For instance I don't know much about today's cases, motherboards, PSUs, Case fans, CPU/GPU cooling solutions, etc, etc.
So, what else do you think I should know about this modern world before I build my new (VR/classic) game rig?
You got some very good answers from our colleagues here.
I can't help but wonder about your "usage profile," or even such things as "what do you do for a living." I was immersed in this technology from 1982 forward, and it's unpleasant for me to think about the cumulative dollars spent -- especially when I made money with my computers. I ate, drank, slept and waked computers until I retired in 1999, and even with that, it's consuming the same time with less intensity since then.
More and more, I watch my money. I have a "preferred account" with a reseller, and except for nickel-and-dime items ( a cable here, a cooling fan there . . ) I gave myself an annual budget and something like a 2, 4 and 6-year plan. I otherwise buy parts in $500 increments, with a 12-month grace period and no payments or interest on each such purchase. I track the purchases online and in Quicken. Instead of waiting until the 12th month to pay off, I follow a schedule to erase the liability before the last purchase grace-period has expired.
They're right about the K processors, and if you're not consumed with focusing on saving chump change, you might want to weigh the pros and cons.
The newer processors are made with smaller and smaller die-size specs -- down from 32nm with Nehalem (2009 or 2010) to 22nm with Ivy Bridge and Haswell. Next year's processors will mean another die shrink.
Thus the voltage requirements have dropped, but since the size of the die has shrunk, removing heat from the processor is still an issue. So the cooling strategy today involves a discussion (see Cases and Cooling) of heatpipe "air" coolers versus water-cooling, and custom-water-cooling versus AiO water coolers.
Suddenly, even mid-tower cases seem to provide more space than needed for storage components, but there is an issue about fitting AiO coolers or custom-water parts to a rig.
First and foremost, pick a good power supply. I think someone mentioned that already. Seasonic is a good choice.
What I'd like to say is "Take your time." I can just imagine that the upgrade gap you hope to bridge could be a temptation to be too much in a hurry.