It seems to me without calibre restrictions for real guns you can improve the range of most airsoft guns, right?
You can theoretically turn any airsoft gun into a DMR. Take a MP5K, throw on a massive suppressor, 500mm 6.01 tightbore, upgrade the compression system, throw on a 4x ACOG, and run .3g BBs, and you have a gun that will match any other airsoft DMR on the field.
For all the guns you're asking about, your best to use youtube and google and find reviews that all already out there for information. It's way better than asking for everyone's opinion on every gun that catches your eye.
Also, if you're actually 18 ("Not being worth my time" is the usual cover-up for 16 year olds that can't get age verified) hold off buying anything until you see what's in the classifieds. It puts retailers to shame the deals you can get.