Well, first of all I’ll just make the point that I do audio-post for a living, not composition and I usually also don’t build computers for other people. So with that caveat:
I think you should consider how many voices you need playing at any given time.
I think you should consider how low the buffer needs to be when you’re recording for real-time ‘feeling’. Some “need” it to be super-small but others can get away with larger buffers. On Gearslutz for example I see people say they “need” 32 or 64 sample buffers and nothing larger will work for them. But on the other hand I have a friend who plays in the bigger live musical theater productions in Stockholm and he runs his rigs at 128 samples.
Figure out if using ASIO Guard helps you use more tracks/plugins and/or lower buffers.
You can then go check out the later DAWbench tests performed for different CPUs. You can punch in a CPU in the top right corner search box * here * and you should get results for the CPU you’re looking at with charts etc.
Please note that DAWbench results have a couple of caveats;
*** Sometimes the testers update the test with a new plugin to increase the load on the CPU. This means that if you compare CPU A with CPU B in 2017 the difference between the two may be different in 2018. Sometimes significantly so.
*** The tests show mostly the difference between CPUs compared on mostly similar computer setups, but the absolute numbers also depend on the interface you’re using since some allow for lower buffers.
*** These guys typically test DAWbench on computers using different DAWs. Sometimes it’s Reaper, sometimes Cubase and so on. IF they use Cubase they typically test with ASIO Guard OFF.
I looked up the i7 3770 and it’s a pretty old CPU. You’re probably going to have a problem figuring out just how powerful a new CPU is compared to it because they just stopped testing the 3770 once it got too old. So maybe what you can do is basically find an old test of the 3770 and compare it to the most recent CPU in that test (let’s call that CPU “X”). Then switch to a later test where X is compared to a later CPU and the 3770 is no longer used. And so on until you get to today’s CPUs. That way you’ll have a somewhat better idea of what an upgrade might look like. I had to do the same going from my old Phenom CPU to my Ryzen 7 CPU (first generation 2017).
Now, if you get up to 600 tracks with that CPU then IF scaling by adding cores had been linear you should be fine with an 8 core CPU. There are now plenty of those. Mine now costs about $200 on sale and comes with a good air cooler included. Intel’s CPUs are generally a bit more expensive but perform better.
If you want to have a bit more overhead you can switch from the more consumer/prosumer platforms to the HEDT platforms which are more for workstations (they sit between the consumer/prosumer and server). For both AMD and Intel you’ll then find chips with core counts starting at 10 cores up to 32 cores!
So even if you lose a bit of ‘linearity’ when it comes to scaling with more cores you can make up for it by getting more than twice the cores. In other words, since no CPU is going to run cool with 4 cores (like you have now) at twice the clock speed, and since getting 8 cores at the same clock speed isn’t going to be a 100% improvement but less than that, you can simply get 10 cores or more instead.
Now, for AMD specifically, I would look at either 8 cores or 16 cores of the latest generation Ryzen or Ryzen Threadripper. I would skip the 2990wx 32-core CPU for now. It’s too new and some reports cause some concern. It might be ironed out in the near future, but sine we’re not there yet.
For Intel I’d say the CPUs up to about 16-18 cores or whatever it is have been tested and they should be pretty safe to choose.
So anyway, sorry for all that text, but I really do think it might be more convenient for you to run a single rig rather than two. You could always register on Gearslutz.com and ask Pete Kaine from Scan what he recommends. My hunch is that he’ll recommend the Intel 8700k for lower core counts, and for people like you if you have the money an Intel CPU with 10+ cores (more expensive). The AMD 2950x I’m not sure he’ll recommend.