Hi Bint
personally I do a lot more field recording than taping. Keep in mind that for field recording and nature sounds one of the most important things to consider is self noise, everywhere: mics, preamp, recorder.
I own and frequently use a NT 4 and am quite happy with it.
Regarding SD MixPre, I had one and loved it. It worked really well with a Sony D 50 plus the NT4 or a pair of (quieter) AT 3032.
If you like, you can listen to some field recordings on my soundcloud page (
http://soundcloud.com/moooose). Please read the notes regarding the recording rig to find out what mics or recorder have been used.
PS. Big bravo to Cadel Evans.