Any cs-cart theme is based on their cs-cart default responsive theme, so you should probably contact cs-cart for changing the way the default theme is coded. Anyway, I also agree with sorinw@gmail.com , user experience is what it matters the most. Some people really get stuck in charts and percentages, and numbers, and google technologies (which is changing very often anyway), that they forget to actually take care of their business itself. For multi-vendor, Vivashop is truly getting close to the look of the big boys (amazon, ebay), this is exactly what cs-cart was missing. No other theme gets even closer to vivashop from the user experience point of view, not mentioning the multi-vendor functionalities. And don't forget that your site does not mean only a theme, a theme is not the solution to all of your problems. A website means addons, server setting, server resources, modifications, images, CDN, caching methods, so there's a lot of stuff that you need to consider when you are testing your site. All of these are different from site to site, that's why users report different performance.
In general what you say is okay .. however the point that i am talking about here is a "Google Insights friendly website", because that may effect your ranking in google search result ... also Google Insights is a good tool tells about the real speed of your website for your end users ..
again vivashop is a great theme .. but the point is about Google Insights theme .. which i could not find under cs-cart ...
again i like both vivashop and cs-cart .. but we need to say the reality