I'd go with the C3 before the C4 Ambassadeur. C4 is a higher speed retrieve, and for what you're likely to be doing with it, the C4 gearing will wear out much quicker. C3 is a workhorse. The Shimano isn't built to take saltwater from what I've been told.
The calcutta 400 is a good salmon sized reel, the 251 is to small, not enough line capacity.
I also like the 6501 C3 Abu Garcia. My favorite for fall salmon, back bouncing, trolling and even sturgeon fishing in shallow water. I've got 6 of these reels.
The Penn GTI 321 is another great reel except it's to large for fresh water salmon....unless your fishing deeper water and need spool capacity. If your trolling and not casting, the 321 makes a good all around reel for both salt and fresh water.
You would likely get better information to help narrow down your choices if you describe your preferred fishing method. Makes a world of difference if your trolling or casting IMO.
Something else to consider is..... like everything, your always going to compromise. Instead, why not purchase 2 reels, a decent ocean reel, Penn 321 GTI and a good freshwater river reel, ABU 6501 C3. If you shop around with sales, you could purchase both for possibly $120 or less.