First, it appears that the i7 4 core intel Mac I use has 8 "logical processors"
So I could run up to 7 clients (one of the processors is reserved - for system?)
I currently run 5, one for each of 3 running puzzles and two for evolving solutions or alternate designs. (I will probably add one more to run Devprev solutions.)
So what Bruno and NinjaGreg writes makes sense. Each "core" is actually two processors so the percentages that show up in the out-of-the-box Mac system activity monitor can show >100%. (I am going to look for an application that shows the logical cores like it does when I run Windows 10 Pro on my Mac external HD)
I'm running the build just released to Main last week (4-4-2017), '20170320-3ecbad1b35-osx_x86-main' (alongside some clients that are still running Devprev)
Possible answers for Bruno:
I am now using the Mac OS Sierra, Version 10.12.3. (I am not updating to the newest version yet… I turned off the notifications for System Updates so that I resist that urge!). So I would recommend installing (on a disk partition or external for testing) Sierra and seeing how the latest update to Sierra and the latest Foldit play together before updating. IF POSSIBLE - do this with OS Sierra 10.12.3 because it DOES work well.)
El Capitan appears to have issues running foldit ON SOME MACHINES - slow performance is the most annoying of those issues. That appears from anecdotal evidence from another Mac user to still be the case (I don't have all the details). And this only gets worse on El Capitan with multiple clients.
With Sierra (10.12.3) installed:
The multiple clients appear to me to run just as fast as single clients. This may be because I have also set up my Mac multiple clients differently from the old Automator one Foldit client running copies. (Which never seemed like a good way to run - there is one log file gathering running info from all the multiples… so what happens if it crashes? You can't untangle the log.txt info for just one client? Illogical.)
http://foldit.wikia.com/wiki/Multiple_Foldit_Clients (scroll down to the info for Mac OS Sierra to see how I set up multiple clients for Sierra (10.12.3)
Caveats:
Running multiple clients for days at a time without periodically closing/reopening seems to be a constant recipe for a system freeze on Macs (since I started running multiples back in 2015 or thereabouts, in El Capitan or Sierra) Good news is that this happens at a wider gap between occurrences using Sierra 10.12.3 and the 4-4-17 Main update.
So as "Housekeeping" every couple days it's a good idea to save your current clients, share with yourself, close and reopen the client. (I suspect this is a symptom of the way that foldit uses the system memory but/and it could be a yet-unsolved bug.)
Be sure to close dialog boxes that might be open somewhere on your desktop as this seems to contribute to these hangs. In fact, the latest was this morning when I forgot to close a Mac crashlog window from several days ago, and found it when ending a script hung up one of the clients (that I'd been running for almost a week contrary to my own "Housekeeping" rules).
If you experience a system freeze: Before you give up try option(alt)-Command-esc to open the Force Quit Applications window before you hard quit… and quit Safari if you have it running, then restart the finder a couple times. This has worked in several instances and can show you what might be hanging the system. If it doesn't work you can force-quit the foldit clients from this window then reopen. If it's gone too far you will be able to move your mouse around on the screen but won't be able to click anything and you won't get the Force Quit Applications window… and you'll just need to touch the power button on your mac and hard reboot. this is why saving and closing clients periodically is a good practice. Good "Housekeeping" will for the most part keep these hangs from happening.