I like the 458, love the 375
Built the 458, 375 and 358. If I was going to build one again, it would be the 375. Unless he plans on running heavy subsonics, the 375 will do everything he'd want.
Go over to the 458 Socom forums, those guys have a ton of information on every variant, every know issue and every known solution.
There are barrels to avoid, the biggest issue is that some manufacturers completely remove the 6 O-clock lug in the barrel extension creating one wide smooth ramp, that puts more stress on the remaining lugs.
It's not a cheap to run chambering, be prepared for deep empty pockets.
It's a great choice for quite a few scenarios, unless you have the poors like me