First of all, welcome.
Secondly, I imagine that you meant to write '.308' rather than '.380'.
In my own opinion - only - the R8 is a beautifully engineered rifle that is completely lacking in any soul. It is difficult to describe, perhaps, what I mean; but it goes nowhere further than being a machine.
The Rigby is based on a Mauser action, with whom Rigby are in bed. It's open to question how much of it is actually made in England, with the cynics - moi?! - suggesting that it's nothing more than a rebranded Mauser proofed in England.
The Mauser diplomat is a very practical rifle as it will allow you to disassemble and squeeze it into an airline standard-sized baggage allowance, which will save you from paying the excess baggage fees.
Don't forget to get quick detachable (QD) mounts for the telescopic sights.
Expect a lot of enthusiasm for the R8 and Rigby.
I'd make two suggestions: consider a Mannlicher-Schönauer stutzen (carbine) in 6.5x54. It does not suffer from the sloppy Mauser pendulum-like bolt and has a very light recoil. Also: don't buy new, and keep an eye open on auctions.