Hopac uses a bounded pool of worker threads, number of which is equal to number of CPU cores (by default). A dangerous thing about this design is that a situation is possible where all the threads are busy doing some CPU intensive work and no other Hopac jobs can proceed. A good solution for this is running such a CPU bound computations on the standard .NET thread pool, freeing Hopac pool for more intelligent work. I found a nice code in one of the older Hopac GitHub discussions which schedules a ordinary function on ThreadPool and represents the result as a Hopac job.
Here is a test with explanations: