i can't tell for sure in general. but thermal throttling will seriously impact sequential read/write, by a factor of 10/20... so, it become slow as a "classic" hard drive.
but, in the other hand, access time and random read/write are still better, even in thermal throttling situation.
sooo, maybe you can feel it in game when big files are loaded.
operating temperature has always meaning for ambient temperature range.
but i agree, it's not always clear. and sometimes, you don't easily get this information.
for the exemple, i tried to find it for my seasonic focus gx650 and found nothing... nothing on the box or in booklet.
you have to go on their website to get it. and it's 0-50°C. and i can assure you, when you load a psu, even 80+ gold, some internal parts can go over 50°C.