Both are top notch rifles, but (for purely whimsical reasons) my personal choice would have to be the John Rigby & Co. Highland Stalker due to the age old Mauser 98 actions which I'm a real sucker for.
Caliber would have to be 9.3x62mm Mauser, sighted in for RWS TUG 293Gr soft points.
By the way, the Highland Stalker isn't offered in 7x57mm Mauser. It's offered in .275 Rigby.
View attachment 645186
The .275 Rigby rifle bolt will not close over 7x57mm Mauser cartridges with the longer bullets above 160Gr weight (unless a competent gunsmith increases the Free Bore which will permit the operator to employ up to 177Gr bullets with impunity).
I have successfully (over the years) taken all the African plains game up to the size of eland with one shot kills from both the 7x57mm Mauser (employing 175Gr bullets) and .30-06 Springfield (employing 220Gr bullets). But shot placement becomes extremely critical on the big boys like eland & kudu when any caliber lighter than .338 Winchester Magnum is employed.
One small observation: Both the John Rigby & Co. Highland Stalker and the Sako Model 85 rifles chambered in .30-06 Springfield have 1:11 twist rates. These are optimized for bullet weights up to 180Gr but not 200Gr or 220Gr. This is not really a handicap for most younger hunters these days, since they mostly prefer 180Gr bullets in the .30-06 Springfield. But my personal preference is for the 220Gr bullet (esp. for Kudu, waterbuck & eland).