the question is not answered by how high the ISO setting on your camera is.... its what your photo looks like at a specfic ISO .... I can go to 1600 on my D80 ... but my pictures are grainy at ISO 800 ... also, I can not use a lens with 5.6 ap in low light or overcast ... handheld.... if I use my D80, I use lenses with a 2.8 max .... on my D300s I can use 5.6 lenses because it has a better sensor.... The D90 and the D80 have the same sensor....

I do not know how anyone can answer your question without knowing the camera you shoot with and the light conditions ....if you shoot Nikon DX, that 10-20 is really a 15-30 .... if you shhot low light(not Dark) .... will you camera handle ISO 800 or better .... I have as a second camera, a D80 ... I am not pleased shooting above ISO 400 .... on my D300s, I shoot over IS) 1000 with no problems .... the lens you are considering has a max apture of 5.6 at 20(30)mm ... so the camera an important consideration when choosing a lens ...

go for the D300s .... it has some more advanced features than the 300 ..... for example .... the 300s has 2 card storage slots .... one cf the other sd .... this allows you to shoot raw on one card and jpeg on the other .... also the 300s has video ....

The D7000 is a better consumer camera but it is not built as strong as the D300s ..... yes, the D7000 his more megapixals but how large will your pictures be ..... as for ISO ... yes it is nice to have available 25000 ISO but 6400 is sufficent in most situations .... also buying a used DSLR has potential problems ..... how will you determine the number of shutter actuations ... shutters wear out .... most 300s are used by professionals ... high number of shutter actuations ... it is expensive to replace a shutter .... the 300s body is about $1700 .... when the 400 comes out it probably cost close to or over $ 2000. ... also the D80 is a good camera ..... you might consider buying lenses with a 2.8 constant f stop

for most of us .... a close focus lens will give very good sharpness at 12 inches plus or minus .... anyway .... most don't know the difference between a close focus lens and a macro lens ... always use a tripod

Stack filters are cheap .... but look closely at your picture .... very little of the photograph is sharp .... if money is an issue ... look at the Sigma 70-300m f4-5.6.. its not a macro but is does acceptable close focus work ...