Print preview colors don't match work window + print sizes

Hi all,
This is my first post here. I hope it's not a duplicate because I did a search and couldn't find results that are similar.:mad:
So I am working on this document and it has silver background. I go to print preview (Photoshop cs3 and cs4 on Vista) and I get color looking more like bronze looking but when I do print, it comes out just like it should (in working mode which is Monitor RGB with Proof colors checked).:confused:

This setting is the only one I've used to make sure image/psd looks exactly like what it should when printing. I tried the default Working CMYK with and without Proof colors but it's still showing me the bronze look instead of silver. I've looked on the net and no exact easy fix for this was found. I really really appreciate any help.:D

Another simple question is regarding size. I'm working on a document size of 17.5 x 8.7 inches and the actual Banners will be printed at size 175 x 87 inches (5 banners each at 35inch wide but combined into a big one). So essentially, I'm working at 10% the size of what the final print will be and my file size is 760mgs. You can only imagine how big the file would be if I work on the actual size.:eek:
So my question is, am I doing the right thing here? Should I use bigger or smaller canvas? Please let me know and thanks in advance.;)

what is your resolution at that size??

RE preview - haven't upgraded to CS4 yet

Not sure what you mean??

you say the size is 17.5x8.5in. what is the resolution??

screen size is 1680 x 1050