Ed Boyle is right about the Williams cars - they made silver aluminum passenger cars that were clones of the original Lionel 2500 series of aluminum cars. I think they made them over a quite a few years, actually. The Williams cars say "Luxury Lines" on the side instead of "Lionel Lines," which of course they couldn't use. Lionel also made some very nice "Lionel Lines" silver aluminum cars in the 90s, which were in the same catalog with a set of Santa Fe warbonnet Alcos (I think it was Alcos); I believe it was the Surfliner set.
Lionel has made a number of the two-tone grey aluminum NYC passenger cars, beginning with the 9594-9598 Twentieth Century Limited set made in 1983-84 (they have smooth roofs rather than the fluted ones in the set you pictured). As others said, I think if you're getting a set of grey cars, without a doubt you're better off getting a set of Lionels rather than another manufacturer's versions, because it's more likely the grey color shades will match your engines. Personally, I like color, and the classic grey cars would be preferable. If it were me, I'd go with that 19171 Lionel set you have pictured, or if you want silver cars, the Surfliner cars mentioned above.
Another choice would be the 15" K'Line NYC Empire State Express cars, which are nice, and have finished interiors, but may be hard to find.(pictures below)