CSS loading methods & best practices

I am working in an .ASPX environment on a hosted ecommerce solution that provides me limited access. I can edit all the pages but most of the core framework is untouchable. I have verified that once directory “CSS” automatically includes all CSS files into the head section of the site structure.

I am using multiple CSS files more or less for allocation/sorting purposes. I have 7 style sheets currently. Some must stay separate, such as Reset.css, etc. I may also plan (in the future) to include separate style sheets for specific browsers IE6, IE7, etc.
My questions are:

1

Should I concatenate all the style sheets that I can into 1 (if possible) to speed up the overall load of the site or

2

Should I only include style sheets that are used in every page in the Head section and all the rest reference in a page-specific way? I did not want to use internal as this will take longer to read as well.

The only issue here is that I was under the assumption that external style sheets should always be referenced in the Head section, however, if I chose option #2 it will reference them in the body of the source code, which I don’t think would pass validation.

These are only my assumptions that I am relying on (you) the experts to validate. Thank you.