Mental stress inducing task Mental arithmetic stress test is used widely to induce mental stress in laboratories. Can this test induce stress to those who are really good at mental calculation or enjoy mental math?
Stress is a very broad term. For instance, I'm doing tests on listening effort using pupillometry. Pupillometry measures pupil diameter which is correlated to stress. More stress means larger pupils. Effortful listening is also a form of stress and hence indeed also evoke a pupil response.  

I'm focusing on cochlear implant (CI) users, and these folks even have a lot of trouble understanding speech, especially in noise. But even in total silence (no background noise, normal 65 dB speech) they need to mentally focus on the task at hand. Hence they have large pupil responses even under optimal listening conditions.

However, normal hearing (NH) folks show, on average, also a substantial response in silence, although smaller than CI wearers.

To extrapolate these findings to your case by drawing the parallel between NH listeners (math proficient) and CI users (math deficient), I can assure you that even mathophiles  do show a stress response, even for relatively simple math assignments.