Been out of the upgrading game for awhile. My plan is to go X99 with a 5930k if they ever come back down to $400. What will give me the best gaming performance, one 980ti or two other cards. For instance two R390x looks to run $100-$150 more than a single 980ti. Is the extra $ worth it? Thanks in advance.
980Ti is now 7 months old into this generation and prices have barely dropped from MSRP. Unless $ isn't a factor, and by your post it sounds like it is or you'd be rocking a 5960X+980Ti SLI, it's better to buy a single high end 980Ti for 1440p and go from there. If you need more performance, you can always resell it and/or get a 2nd 980Ti when prices on it drop. If you are gaming at 1080p/1200p, then a single 390 is more than enough. BTW, 5930K has no tangible advantages over 5820K unless you plan on running
3x NV GPUs in SLI. The extra PCIe lanes on the 5930K are irrelevant over the 5820K version in single or dual GPU setups.
Something for you to think about is Intel will release Broadwell-E around June 2016. Also, if you aren't overclocking, i7 6700K > i7 5820K/5930K. I'd only recommend X99 if you will overclock.
Finally, if you also need a monitor, then you should also consider FreeSync vs. GSync. In many cases the GSync monitor is much more expensive or alternatively, sometimes it's simply impossible to find an affordable high-quality GSync monitor but a FreeSync version exists even in
lower price segments.
There are other factors too - how long do you plan on keeping your GPU? Are you OK buying and reselling PC parts to upgrade again?
I'd recommend 980Ti SLI / Fury CF if you are going to be gaming on a 1440p 100-165Hz monitor / 4K. So you kinda need to figure out the monitor first and go backwards.