I'm thinking the cache may be more important than app launch and boot times.
i would agree with that. if your projects are small enough to fit media and cache on the m.2, that would be another option as its fast enough to handle it.
I disagree with RoninEdits and would choose the 512GB Samsung 950 drive and use it for OS, programs, as well as scratch and cache.
I don't have any M.2 drives yet, but use SSD RAID 0 arrays for OS, programs, scratch, and cache and it works great. Today's new M.2 drives are so fast that the rest of your system, especially the CPU(s) are most likely to be the bottleneck with PPro CC 2015.
Thanks. I'm not quite there on cost/capacity for SSD media storage. However for remote edits on laptop I've been sticking SSDs in USB 3 cases. But at the office, most of my projects average between 500GB-2TB of total disk usage (each), and I often have 2-3 running at any given time. I have a 4x3TB RAID 0 and a policy of daily or twice daily redundant project backups in place to handle that.
In general, I've always configured my system drive (OS/apps) as one device, media sits on another device (typically spinning disk RAID), and Global Performance cache on a third device. For the past 5+ years, only project media was on spinning disks. The conventional wisdom on separate cache and system drives has generally been performance-driven. Each would be free to handle it's own data traffic. While definitely true of moving-head spinning disks, it was also (kind of) true when they were both SATA SSDs, but to the possibility of data bottlenecks at certain times in the course of working a project. But with the advent of super-fast M.2 PCIe x 4 devices, I'm thinking that device separation requirement softens quite a bit, as IOPS and available bandwidth are so high it's likely there wouldn't be any bottlenecking at the device.
In my case, because the biggest Samsung 950 I can get is 512GB, I'd really like to give the whole thing over to AE Cache, and not tie up it's capacity with ~80-90GB of System OS/Apps and stuff. The question I still have mulling around in my head is where to put the pagefile and whether to kill the hiberfil.sys, which on a machine with 128GB (or even just 64GB) RAM can get pretty big on a boot drive.
FYI I've actually got a couple of build projects mulling. This one we are discussing would be a next-gen CPU upgrade within a few months from now when new i7 x part ships. But the other is a simpler small portable rig in an ITX case for remote work that the laptop just doesn't have enough grunt for.
JEshorts option is valid too. the options are only limited by the space needed. i wouldn't agree with it being a better option since media and cache drives are more important for performance, than a fast os/apps drive. once the 1tb and larger come out, we may be using a single drive for everything. hopefully samsung will start offering pcie card ssd's like intel does, then we can get away from laptop m.2 drives in desktop computers, and not have to worry about only having one m.2 slot or using pcie card adapters.
i would disable hibernation.
for a small x99 itx build, it will depend when you build it, as the 1tb stick might be out. if not or 1tb is still not enough, then JEshort's option of using the m.2 for os/apps/cache would reduce the drive count by one, and allow large sata ssd's for more capacity. in a small itx case that might only hold 1-3 drives, that could make a big difference.
and if we are talking about future pc's in 6 months to a year from now, we may be beyond these slow m.2 drives from samsung and onto new drives from intel. so this whole conversation and build design may be moot.
For a 128GB build I would suggest skipping the pagefile altogether and turning hibernation off.
If you are even remotely concerned about 512GB not being enough for your AE cache, possibly you should consider going with an Intel 750 1.2TB. They have really dropped in price recently; Micro Center is selling them (PCIe or 2.5" U.2) now for only $649! While the M.2 stuff is definitely the speediest option now, Intel's larger, better cooled drives do seem to be more reliable.
All sounds solid and good. Except have you seen the specs on the Samsung 950? I wouldn't exactly call 2500MB/sec and 300,000 IOPS "slow M.2" as it's pretty close to the fastest thing going and darn close to the Intel 750. Samsung SSD 950 PRO Specifications | Samsung SSD
As far as when the builds? I think the mini ITX is going to go forward first (December) with an X99 Asrock mobo and a 5820k (28 lanes OK in an ITX build). The Desktop will be a major worstation upgrade with the next gen Broadwell-E i7 X CPU (the successor to the 5960X) which I anticipate in Q1, 2016. Sounds like it will still be an LGA 2011v3 part utilizing X99 platform. But it will basically be a rebuild of my current 3 year 3930K/64GB rig and next time probably go 128GB budget permitting. Of course CES is coming and might bring new mobos but if I picked one today it would probably be the Asus X99E-WS, which has only 1 M.2 x 4 slot. Maybe there will be a new workstation class mobo with two M.2 slots and no other compromises by then.
the "slow samsung" comment was made kinda joking/sarcastic, not as they are really slow, but will be slow in comparison to what intel has coming. i think broadwell-e is planned for q2 2106.
Well I am pretty much planning to be not just dead, but really, really dead in q2 of 2106, so no worries for me and the m.2 I just bought.