For the ultimate express rifle,like others have said it just depends how much money you have. Two ways to go,using a Mauser clone action,which would probably be a action made by GMA in Arizona,a Satterlee made by Stuart in Deadwood South Dakota, or a european clone made in Germany by Prechtl or FZH.
GMA is going to be about 3500.00 and will not feed straight from the box and require finishing by your riflesmth. The Satterlee will feed straight from the box and be about 98 pct finished,but Satterlee delivery times have been spotty and long times for delivery. Both are excellent actions.
You can contact Montana Rifle (MRC) as they make Mauser hybrids also. Another source is Wayne at AHR who specialises in custom CZ actions and rifles.
You can expect to spend a minimum of 10K to 12K on a fine Mauser rifle done right. Whether going with a clone or an original M98 Mauser action that has been reworked for the specific cartridge.
For the 375 Holland I used a model 70. I would use a M98 on anything smaller and for Express I used the actions below.
2 Satterlee magnum Mauser actions 416 & 450 Rigby