the higher res will slow things down and some people say at those res's you can lower or do without AA but it comes down to personnal preference.
as to wther you can lower your res with that LCD, it depends on how well it scales. what options does your monitor have. can you choose between fill, maintain aspect ratio or 1:1 pixel ratio or just the first 2. if you can do the latter then it won't decrease visual quality, however the other 2 especially the first will leaad to a slight and probably imperceptable reduction in quality.
basically, i would try out as many different settings as you like and see how it looks as that is all that matters.