Can someone please give me the pros and cons of each caliber. I know the No. 2 generates less pressure due to the large case but I think it is somewhat more expensive. Ballistically it is a dead heat with factory rounds but each could be juiced a bit for a Ruger #1. Thanks.

The #2 version is a longer case, and also the brass is thicker, both in body and rim. However, I have not seen much 450 #2 brass available, except Bertram, which I would stay away from. BELL made it at one time, but I didn't see it on their website. The standard 450 NE can be loaded up approaching 2400 FPS in the Ruger #1.

I've got both. One a Jeffery 450 #2 and the other a WR 450 3 1/4. The #2 is a lower pressure cartridge and the cartridge sounds really cool dropping into the chamber, a deep thunk. The drawback to me is a thicker action because of the larger shell.

The WR is a much daintier rifle, narrower. They both shoot the same but I would guess the #2 could hold much more powder in a Ruger.

Homebrew
I have a 450 No2 double rifle. The Bertram brass is more expensive that the 450 3 1/4. I have brass that has been loaded at least 15 or 20 times, I did not keep count as I did not expect it to last thet long. I have some that has been loaded 7 times that I am "counting", that still looks new. I do not know how the brass would hold up at the higher pressures possible in a Ruger No1. I really like my 450 No2 double.... But if I was "doing" a No1, and did not have a British double, I would get a No1 in 458 Lott. The only logical reason to have a No1 in a British calibre is if you have a double rifle and want a scoped single in the same calibre. However if you "must" defy logic, either 450 would be a good choice. I would base my decision on the info from the gunsmith making the conversion.