SEO for 2 websites in the same niche market

I have 2 websites in the art market. SITE NO 1: 7 years old pr 5, ranks between 6-8 on page 1 of [login to view URL] for my most important keyword (phrase is keyword1 + Art). This keyword is a fairly niche keyword, returns results of around 2,600,000. I will provide respondents with the additional keyword for the exact phrase. This is an informational website which has been positioned as an authority on the niche market but at the same time has "sales style" information to get people to click on the link to the online shopping cart which is on a separate domain. I want to get this site into the top 3 or higher. I can't seem to get it any higher than where it is now. SITE NO 2: Same market, same important keywords. Site is 3 years old, domain is 6 years old. It's the online shopping cart / online gallery for the site mentioned above. Has over 1000 artworks online plus a bunch of unique content separate and different from site number 1. It has enough to stand on its own as a website and not just a shopping cart for site number 1. It has a pr 4. It ranks very well for lots of niche terms but for the most important 2 word keyword (same as SITE NO 1) it ranks page 15. It was as high as page 3 a year and a half ago but has steadily dropped away and continues too. I can't work out why. For keyword1 + Art it ranks page 15. For Authentic + keyword1 + Art it ranks page 1 number 4. For keyword1 + paintings it ranks page 1 number 7 and is higher than SITE NO 1?????? I need a SEO master to work out why and to turn the site around and get it on its way to the top 10 of google for this important 2 word phrase whilst not sacrificing the good rankings it receives for lots of other phrases. Only seo experts need apply. I have a reasonable idea about SEO so i need someone who is much better than me. Strictly White Hat SEO techniques only (Black Hat/ Grey Hat Techniques are not allowed at all). I can't stress this enough. I'm not interested in risking a google penalty at any cost and I know what black/grey hat techniques look like so please don't apply if you push the boundaries to the point a penalty is possible. Examples of success / SEO ranking increases with other clients is required as well as details of your background and seo experience. The more real client examples that can be quantified the better. Look forward to talking with you.