With such a hard kicker, you want the most eye relief you can get. I have an Elite 4200 4x-16x-50mm on my 7mm Ultra mag. It has I think 3.6" and has not cut me yet, but the 300 ultra would kick harder.
Ironically, there was an article some time ago and the author was using the Nikon Gold scope you are looking at with 4" of constant eye relief on top of the 300 Ultra mag. He loved the scope (and I do too as I own several monarchs).
All the scopes you mentioned are good scopes. The Elite 4200 2.5x-10x-40mm, of which I also own, has way too little eye relief for what you need. Same goes for the Swarovski.
I'd say go with at least the Elite 4200 4x-16x-40mm or 50mm AO. This is the most bang for your buck. Of course the Nikon Gold and Zeiss Conquests are also excellent scopes as well.
Zachary