Whenever you build a quality rifle I would recommend a factory cartridge for availability in the field and for resale value. There are very few wildcats that are superior to factory cartridges for a hunting rifle. When someone picks a Mauser 98, instead of a Remington, Winchester or other action to build a gun from scratch it is only fitting that he selects a proven cartridge.
The .416 Ruger is superior to the Taylor in that it can produce the same velocity at lower pressures or more energy if needed. You can pick up a box at your local dealer and dies,cases and bullets are readily available at reasonable prices.
The.375 Ruger is a better choice for the 98 than the H&H because the action does not need to have any metal removed from the front receiver ring.( The .375 Dakota is slightly better but cases and dies are expensive).
For the Purist a .404 NE can be shoehorned into a 98 as Jeffrey did with his classic guns.
With more expense a .400 H&H .465 H&H can be adapted. They are newer rounds,2003, but are shorter than the .375 H&H.
A competent smith can even fit a .416 Rigby into a 98 by removing most of the metal from the rear of the action and limiting the COL to 3.6".

My personal choice would be the .404Jeffrey but again it depends on what you hunt.

The only Wildcats that might make sense for a DGR are .458 to .510 cal that use a larger diameter case than the Win. Mag.
The 450 G&A, .450 Rigby 2.5", the .458AR (Accurate Reloading)and the .460 A square(No longer in factory production)have no factory equivalents probably because a handloaded .458 Win Mag with a 480gr Woodleigh at 2150fps will do the job.