My CPU has 4 cores, each capable of running 2 threads for 8 in total.

My BOINC settings regarding this are:

On a multi-core system, use at most 1024 processors
On a multi-core system, use at most 50%
Maximum CPU time usage 30 %

And in BOINC manager: Use GPU always.

BOINC appers to use 9 calculation threads when running. During its 30% duty cycle bursts it uses all 8 cores (or according to itself 8 + 1/32th CPUS! and one GPU).

Forgetting about the "1/32th CPU", to use half the cores and as much GPU time as it wants, what should the settings be? Should I simply say use at most 4 processors and have different profiles for different machines? Thank you.

My CPU has 4 cores, each capable of running 2 threads for 8 in total.

So a Quad core with hyperthreading, making eight cores total.

My BOINC settings regarding this are:

On a multi-core system, use at most 1024 processors
On a multi-core system, use at most 50%
Maximum CPU time usage 30 %

You don't say what Boinc version you run, or what website you set your preferences on,
the most recent Boinc's and website preferences only have two settings:

Computing Usage limits
Use at most 100 % of the CPUs
Use at most 100 % of CPU time

The other setting was for Boinc 5 clients, and is no longer used.

And in BOINC manager: Use GPU always.

BOINC appers to use 9 calculation threads when running. During its 30% duty cycle bursts it uses all 8 cores (or according to itself 8 + 1/32th CPUS! and one GPU).

Forgetting about the "1/32th CPU", to use half the cores and as much GPU time as it wants, what should the settings be? Should I simply say use at most 4 processors and have different profiles for different machines? Thank you.

Use the term 'Tasks', Boinc will run enough tasks to occupy all your CPU cores and GPUs, subject to your preferences, and the application's requirements,
each application may have more than one thread running, the OS or the app will decide which cores they'll run on,
Boinc can run non-intensive applications too, adding to the number of Boinc related threads running,
so don't use the term threads unless you're counting them up in Task Manager or the like.

Claggy

BOINC version is 7.6.33 (x64). OK, in BOINC terms a logical processor = a CPU, which makes things easy. If I set it to use at most 50% of the CPUs in BOINC itself, then it uses 4 CPUs.. perhaps with the occasional 1/32th CPU thrown in - don't know yet, but not a problem in either case.

The preferences were set through "BOINCStats BAM" and climateprediction.net before.. so that is now obsolete? Thank you.