Why not just try it and see? If you want to know the numbers. Use a temperature monitor with it on the desktop for a few hours/days so you have some data. Then move it to the cabinet and repeat checking the temps.
In the end, if it works or fails is what matters, not so much how cool or hot is gets. It's very unlikely any permanent damage will occur if it gets too hot, and if you get issues, crashes and shutdowns then you know there is a problem and you have to move it back to the desktop.