That will be nothing wrong until you reach and use with 90c all the time.
Also, the main problem is
not the GPU temprature; it is VRM. Do not trust 60 degrees. Check your VRM temps.
79 Degrees at 99%
Edit:
The above was "off the shelf" settings.
Using the fan curve feature in MSI Afterburner I set the GPU fan speed curve to max the GPU fans out @ 70 degrees.
With this new temp curve in place I can maintain a temperature of 70 degrees (+/- 2) while @ 3,400 Mkeys/s but the card alone is consuming about 435Watt
2nd Edit
After removing the glass side from my PC case leaving the chassis open with a small external fan blowing into the case the card runs @ 3,422 Mkeys/s while maintaining 60 degrees (+/- 1).
The manufacturers documentation for my case states the case should be closed to maintain correct air flow however all temperature readings on the system suggest otherwise, the entire system is running much cooler, the GPU 20 degrees less on average.
So the FINAL answer to the original question is
The Zotac RTX 4090 running Bitcrack2 can process 3,422 Mkeys/s while maintaining 60 degrees with a fan speed floating between 65 to 68%.