Eh? What you state about ls, wc and less is directly contrary to my experience. I'm so astonished I created a 30GB test file and tested it:

     $ cmd /c dir k.txt
     Volume in drive C is CobraRoot
     Volume Serial Number is 02D8-502C
    
     Directory of C:\Users\barrkel\AppData\Local\Temp
    
    2012-07-01  15:24    31,292,160,000 k.txt
                   1 File(s) 31,292,160,000 bytes
                   0 Dir(s)  142,087,471,104 bytes free
    
    $ du -h k.txt
    30G     k.txt
    $ ls -l k.txt
    -rw-r--r--+ 1 barrkel None 31292160000 Jul  1 15:24 k.txt
    $ wc -c k.txt
    31292160000 k.txt
    $ time wc -l k.txt
    6400000000 k.txt
    
    real    1m5.651s
    user    0m46.207s
    sys     0m8.642s

66 seconds to read 30GB isn't too bad, that's over 400MB/sec. (It's an SSD.) When I said directory listings could be slow, I meant directory listings, not general I/O; simple read() and write() do not need translation (provided you aren't using Cygwin text-mode mount options, which are not recommended).

    $ less k.txt

this works just fine; when I do > to go to the end of the file, it goes there immediately, but stays busy calculating line numbers (it's scanning the whole file); if I cancel with Ctrl+C, it stops, just like it does on other Unix OSes.

PS: It's the mingw tools that don't work properly! I tried it a couple of times, but all the incompatibilities made me give up pretty quickly.