RE: Given these choices?
I assume his Model 98 is in 8 X 57, and he has a Swede in 6.5 X 55 right?
If that be the case I would recommend he go for either the .308 or the M44 in 7.62 X 54. Both rounds are comparable. He should get whatever he wants, but if he picked between those 2 he' d be filling in between his other 2 guns.