Let’s go!
I’m going to talk about differences between the functionality of the T2 and slim stem:
The slim stem is simple, and uses the high cooling helix you could use on the t2 stem, but the t2 stem doesnt get as hot as the slim one after one/two heats up. The fins on the t2 stem and the form factor of the shield and middle part help a lot on this purpose. This makes the vapor cooler too.
So i would say the slim is great when you are used to do 1-2 heats up and done (or let it cool down). The t2 stem gives more play.
The slim is more sexy, but the t2 can be as well if you get nice shield.
Now, the head:
They will be similar (the 1/4 chamber of the ss will be on the t2 too). The main thing you have to focus on, is in the material you use inside the head.
If the Ti works great with rubi/zirc, since the ti transfer the heat faster and those materials balance it out… the ss one works great with quartz balls, since the material which keeps hot is the ss. It works really well with quartz.
So, if you use ss, you will find the fast heat up materials as a good choice, and the oposite for the Ti version.
Now, the cores. In principle, this isnt like the balls, i would say the ti core and the ss core works better on the ti version. Depending on the heat up time you want, or the heat retention you want, you can use any of them on the Ti (i didnt try to combine them 
).
In case you want to use the core on the ss tempest, i would use the ti one.
I would recommend the ss core + ss tempest for the people who want a slower heat up time, using (max) 1-2 flames….letting it cook. That way you get a more hybrid results with a lot of retention, killing 0,2/0,25 without problems. BUT, you wouldn’t want another heat up with a slim stem until the full device is cool.
This is just my experience.