Use LibreOffice, it's much better than OpenOffice and better than Excel if you have an AMD GPU, instead of Ubuntu use Xubuntu or Lubuntu, that way you'll be saving a bunch of processing power that you can use for when you're 3D modelling or gaming (I mean, you'll already be doing that if you use Ubuntu compared to Windows 7, but still, you might as well go all the way right?). Ubuntu/Xubuntu/Lubuntu also boot waaaaay faster than Windows 7.