At our institution we have independent call. So sometimes, some calls are really hard to make ( Like a closed loop If you overcall it the patient gets a surgery he didn't need. If you don't call it, then the patients ends up with bowel necrosis). So there is some nerve wracking situations, but it's good to experience this while somehow in a safe setting.
For me, the big thing that is stressful is the constant phone calls. During peak hours, we have been receiving something like 15-20 phone calls an hour. Sometimes, these are situations that require some time while the list balloons.
I would say that if the phone calls were taken out of the equation (protocolling, contacting providers to tell them that they ordered the wrong study and what not, OKing a study, walking a provider through a ****ty read etc...), then call would not be that stressful, at least not out of the ordinary. Sure the volume can be daunting. I just had an unusually busy evening evening shift for 4.5h, ended up reading 29cts, 1MR, 5 US and 49 radiographs (I have had entire nights were I read less) but if I didn't have to constantly answer the phone, then I would feel more confident before signing the study, particularly when things are this busy. I probably would not go any faster, I don't think I can, but I think I would feel safer. This is what really adds to my stress while on call.