I have a .375H&H and a .416Rem that I have never really used.

I am just thinking about trading it for something in .458Lott, good idea? Actually checking out the "national catalogue bank" the only rifle I would go for that is availiable here is the A-Square Hannibal but I have a nasty feeling they are rather pricey over here...

What do I stand to loose?(aside from the inevitable$$$)

Unless I am really bored wit ha caliber I do not sell them. If I had a .375 and nothing else I would get a .458 whatever but I would not sell my .416 Rem to get it. I would just get the lott and keep both your other big bores personally. as you might regret it later.

PC is correct. Go out and use that 416 Remington. It might just impress you enough to hang onto it. The Rigby with the same velocity and bullet weight has been doing it all for eons.
Take care,
Dave