Do not use JCHOptimise - it wrecks more sites that it helps... I've seen this so many times!
No, I think your problems are a really, really, slow server.
You have left a lot of other images and overlay in places and stacked a load more over the top...
try this too...
div#rt-main-header {
background-color: transparent;
}
that will get rid of the green before your image get put on the top. But this doesn't fix your sloooooooow server.
This is how to create a custom CSS compatible with Gantry 4...
Simply create a file called "<TEMPLATENAME>-custom.css" and put this file in the CSS folder of the template (where <TEMPLATENAME> is the name of the template as seen in template manager e.g. rt_fracture). GANTRY4 will automatically load this CSS file. If you wish, you can also have browser specific files by appending, for example, "-ie9" making the filename "<TEMPLATENAME>-custom-ie9.css"
Regards, Mark.