Memory utilization at 98%, why not 100%?
Everything requires memory including the OS just like SQL Server. The Operating System can remove memory from SQL Server, unless you happen to have locked pages in memory permissions for SQL Server. However, even then the OS will always win to keep itself running, so if it needs memory it will force SQL Server to give it up. 

As well, just because SQL Server pulled up to 98% memory does not necessarily mean it is using it all. You would have to dig into memory usage of SQL Server itself to know what it is doing with it all. It holds it until the OS request it back, forcefully or in a nice way.

I will also note, you should not have max memory set "well beyond the server's current memory" capacity. SQL Server thinking it can grab more memory than there is really is can cause performance issues. Max memory is just the buffer pool limit, this does not include other areas of SQL Server processes that grab memory. So it is best to keep the max memory lower so the OS and other processes for SQL Server have some.

To dig into into performance, use Perfmon, DVMs, your monitoring tool (if it includes SQL Server monitoring).

Specifying Max memory: I base it on the OS but you also have to consider what else is running on the server. Are you running other components of SQL Server (SSIS, SSAS, SSRS)? Do you have any agents for monitoring or security purposes? An example, base value for me with Window Server 2012 R2 is leaving the OS 6GB of RAM and everything else goes to SQL Server.

See Monitor memory usage in the product documentation.