You need to decide on what you plan to hunt. The best factory rounds for the Mauser 98 are:
9.3x62
.375 Ruger
.416 Ruger
.458 Win Mag.
With more mods and expense.
.375 H&H
.404 Jeffrey
If you Handload
.400 H&H
.458 AR
Have more money to blow?
.465 H&H
.500 Jeffrey
Read up about these and see if there is a local smith that can put one together for you.
For a useful all round rifle you can use on elk and big bears .375 Ruger.
For Buffalo in Africa .416 Ruger.
For A classic pre-war style .404 Jeffrey.
To be the only kid on the block,(or in your State)with one .465 H&H
Max power with a classic .500Jeffrey.