Nikon 4300 or Nikon 4500 or something else?

Does anybody have some advice on which of these two cameras I should consider getting, for general usage and mucking around with my telescope (planets and brighter DSOs)?

The 4300 has a bulb of up to 1 minute, and is up to ISO 400.
The 4500 has a bulb of up to 5 minutes, and is up to ISO 800.
Both have some noise elimination feature for long exposures.

I recollect reading here early this year that the previous models of these cameras required some extra gadget to get the higher bulb exposure times, and someone saying that the gadget shook the camera, making the long exposure useless. Is this still the case?

Do the differences in ISO make a difference?
Do the differences in bulb exposure time make a difference, or does the noise negate it?
The 4500 looks like it would be more awkward to use or more out of balance than the 4300, if it is attached to a telescope with a Scopetronix device. Is this correct or am I mistaken?

I would appreciate your advice, as the only thing I know about digital cameras is what I've read. I've only ever taken one shot with one. If you can advise me of something else to consider in the same price range or cheaper, please let me know. Thanks for your help.
Renato

The 4500 has way more manual settings than the 4300. As for noise, any CCD w/o a Peltier cooler will produce a lot of it, but you can pretty good results by doing a dark subtraction in Paintshop/Photoshop..etc. As for balance issues, the 4500 is very light, shouldn't have aproblem. The nicest thing, is that when you have it connected to a scope, you can twist the other half to a comfortable position. I don't believe the 800 ISO setting would be of much use on a long exposure due to too much noise. You can look at ones like the Canon S30..etc, but the Nikon is a great camera.

I took your advice and ordered the 4500.
Renato