For your site, since you have a logo which is slightly taller than the one on my site, you can prevent floating menu by just using this custom CSS. There is no perfect sized logo as such. It all depends on nature of the site, client needs, brand and hence we need to tweak the code a bit to achieve that perfect layout –
#header.sticky #primary-menu > ul.menu > li > a {
line-height: 100px;
}