Yeah, Intel and Apple consider it “performance left on the table” if you’re not pushing against the TJunction, which is 100C for that chip. - It will emergency shut down if temps are dangerous and of course turn down speeds and up fans before that. Fan can actually go to 3600RPM, even though 2700 is the “max”. If it thinks the temperature is too hard to manage it’ll go that far, and if it still can’t keep it down shut down on its own.
Can you measure a performance difference in tests? The CPU difference may just be smaller than you expect. Or may just not matter in the types of tasks you do.
For that specific model iMac, if you have the R9 M295X, be more wary of its temps than the CPU. Though looks like you have the 290 so it may not be a concern at all. My old R9 M295X could hit 110C even without pushing it 100% and it eventually killed the system. (my new iMac is much better thermally)
As long as you actually benchmark within expected values for a Devil’s Canyon i7 iMac, I’d say you’re probably hitting exactly what’s to be expected. If you’re actually benchmarking significantly lower, well, yeah might need to make sure there’s good thermal contact with the heating and CPU and fan is set properly and all
