I don't have the specs for the engine question, but the Rolls-Royce Web site has a lot of data about their engine line. They give weigh data for some of them. I heard that about 75% of the 757 sales are R-R powered, I think because they're more fuel efficient than the older PW fans. The current RB211 model that is being used now is newer than the 757 itself. On some of old pictures of 757s, you'll see a R-R engine that looks a just like the RB211 on the L-1011 or the 742. I think that just about all the airlines that ordered the early R-R fans (mostly BA) have replaced them with the newer R-R fans.
Also, most airlines do not operate the 757 across the Atlantic unless they have to (except Icelandic). For example, Continental operates 757s to Europe now, but they announced that the 757 flights will be replaced by DC-10 flights as soon as they get enough 777s to cover a few more routes that are currently flown by the DC-10s. The trans-Atlantic range is just a handy little feature of the 757 that allows airlines to expand their overseas markets even without having to worry if they have enough widebodies to cover all the routes.