nobody answering this one, cause I guess there is no clinical answer. Given the aluminium heat sink size and the bay area of most computer cases do not get a lot of direct airflow, I guess they would normally be fairly hot. I brought the optional water block and added them to loop.

Now as my motherboard Vregs are no longer water cooled I found they were running at 60+ C, after putting in a silent low speed 120mm rear case fan and a square of cardboard to direct airflow pass the Vregs, they now operate between 30 -40C. I guess if you are concerned that the amperage through the Vregs will shorten their life, perhaps consider direct air cooling.