I am always looking out for M98s. The best ones for my purposes are the rifles with rusted bores and cracked stocks, but unmodified actions.
I think the M98 Mauser from various makers is still the best all-around action for custom gunsmithing for nearly all bolt action purposes except for left hand guns and for shells with a smaller head then the standard 57 MM Mauser case. They don't make for very good 223s, and you max them out with the 404 Jeff and 416 Rigby size.
I have owned more Mausers bolt action that any other make over my years of gunsmithing and shooting. I currently own Mausers from 25-06 to 404 Jeffery. I have had 458s and 460s too, but I sold them off years ago after I had a period of 3 years in which I never fired a shot from them. I realized that everything I'd ever want to do with a powerful rifle from that point on in my life would be does as well or better with my 375H&H or the 404.
The largest caliber I have ever made on a Standard length Mauser is a 416 Rigby. I have made 460s and one 505 Gibbs, but they were made on Magnum Mausers, not military actions.
Other Mausers I have made for myself and loved at times have been some in 6MM Rem, 257 Roberts, 6.5 Swede, 7X57, 30-06, 308 Win, 300 Win Mag, 308 Norma mag, 338 Win mag, 338-06, and 416 Taylor.
I have also owned and used the 7X57 and the 8X57 in full military configuration. Today if and when I find unmodified military rifles in good shape I am loathe to do anything to them but shoot them. Unmodified Mausers are getting rare. But most I find have already been modified and so going from a "Buba" to a full blown custom rifle is a step in the right direction, not the wrong one Taking a $175 rifle and turning it into a $1500 - $2500 rifle is good. Taking a $600 rifle and turning it into a $200 is not.
As a side note, if asked "how accurate can military Mausers be?"
Well this is my full stocked 8X57. The barrel is a cut down and re-contoured military barrel. Made to look good, but the inside is unchanged since the day it left the Mauser factory.
OLYMPUS DIGITAL CAMERA by
Steve Zihn, on Flickr
OLYMPUS DIGITAL CAMERA by
Steve Zihn, on Flickr
Here is how well it shoots with some Speer 200 grain bullets.
PC070001 by
Steve Zihn, on Flickr
So, if you get a Mauser with a good bore, you can expect it to shoot better than you can with the irons sights. Not all are 5/8" shooters, but I have not seen a good (meaning not rusted or damaged) Mauser barrel yet that would not hold under 2" and many like this one go WAY under.