etx-125 with nikon 5700

The 5700 is known to be 'slow' and needs lots of light to work well. I plan on shooting both sky and wildlife (birds, small animals).
Is the ext-125 a good choice?
I just bought a etx-70at and I can tell it was not a good choice.

Just my opinion, but...

In that aperture range, and with sky and wildlife shots as a big part of your planned itinerary, I'd be more inclined to put the money into a quality small refractor (preferably an APO ~f/6 and 85mm to 130mm in aperture).

Your coupling method will be afocal (as the CoolPix lens is not removable) and the optical zoom will easily allow you to increase the image scale sufficiently for targets reasonably within your grasp, but a higher f-ratio (and central obstruction) will limit the lower end of your range. 5" of low f-ratio aperture can provide woundrous views of wildlife and celestial targets as well as stunning shots of solar system targets with the appropriate eyepieces.

You might want to visit the Digital Astro egroup for more info:

http://groups.yahoo.com/group/digital_astro/

Paul