No, you cannot. A given task, running at maximum "niceness" (i.e., the lowest "priority" in regard to its peers) will happily consume 100% CPU if it has enough

No, you cannot. A given task, running at maximum "niceness" (i.e., the lowest "priority" in regard to its peers) will happily consume 100% CPU if it has enough work to do - at least in total absence of other consumers of that resource. SIGSTOP effectively tells the scheduler to just not allocate any CPU time to the task any more, which makes the task unable to perform any work (and also not consume any additional resources, of course).