Try the Custom New Tab extension.
Set the page you want for your new tab, and then Ctrl T or Ctrl N will take you there.
For when you open the browser, go to Settings (Alt P), the Browser tab, and On Startup, and set what you want if you don't want the speed dial there either.
Another possibility for an extension is Home Page in New Tab, https://addons.opera.com/en/extensions/details/homepage-in-new-tab/?display=en
though I haven't tried it.
Use Opera 12.16 or Older versions for now.
Opera 11.64 has fewer issues with skins than Opera 12.xx, which is one of the reasons I am still using it. See the skins link in my sig for more.
Opera 18 is not ready for use yet — at least not for long-term users who are accustomed to a high degree of customisation in Opera. See the Customising forum for more details.