To add RAM you'll need to pry the case apart and remove the screen entirely. That's not what I'd call "user-serviceable," and Apple agrees. If you start tinkering with these parts, you'll almost certainly void your warranty.
:-)
The most notable is that the iMac's RAM isn't soldered directly to the motherboard. That means it is technically replaceable down the line, something that hasn't been the case in a 21.5-inch iMac since 2013.
Huh.
I replaced a HD in an older iMac, (two actually) so I already have the suction cups! (Mind you I think they use glue now)
RAM isn't accessible by the user anymore. You have to open the chassis.
Vincent says it's fast. Very fast. http://blog.vincentlaforet.com/2017/12/12/apples-new-imacpro-has-an-impressive-200-300-speed-bump/
For example system on two used Xeons (or even AMD) + GTX Nvidia card + 40" 4K Samsung TV are also very fast. Just cost around 4 times less.
AMD RYZEN Threadripper based system is more, but also not too much.
does it run FCPX and Logic Pro X?
If you install Hackintosh it does.
You could also, in theory, get an older Mac Pro (5,1) - it looks it can run with dual Westmere X5690's (6 cores @ 3.46 ghz). In that config, it can take more ram than either the trash can or the new iMac (128GB for the newer ones, 160GB for the older one) and you can put an off-the-shelf GPU in it. Apparently there are some power-related shutdowns with the 1080ti (unless you use external power or poach it from SATA), but dual 1080's work OK.
I got curious so I did a little poking around on ebay:
So that'd be 12 3.46ghz cores with 64gb of ram and 2 gtx 1080's for a total of about $2919 - and it'll run OSX without hackintosh. That's not too bad.
I would purchase a new proper "Mac Pro" providing it was actually upgradeable. In regards to purchasing a used Mac Pro 5.1 at the end of 2017 it is simply not worth it IMO. I have been running a hackintosh for about 3 years with no problems at all. The main thing I do to prevent problems is to hold off on the OSX updates for a couple of weeks. You could build your own Hack Pro for about $3K that will last you a lot longer and also outperform the Mac Pro 5.1 in many different ways with more flexibility and overall bandwidth.
iMac Pro = I will pass not interested at all. IMO Apple is complacent FULL STOP.
Here are two different configurations that allow you a lot of flexibility in terms of price/performance and flexibility.
It looks like you're new here. If you want to get involved, click one of these buttons!