upgrade from 400d and all round lens for it!

Get the 50D because you will be able to find it for a better price than the 60D.  Make sure you're buying it from someone with good reputation.

I agree with Philip-Davis.  The 50D should keep you busy for a while.  The 50mm you have is a great little lens, but might be too tight on a cropped sensor body for general use.  I use the 35mm f/2.0 almost 100% of the time.  As far as your long glass...  You may want to upgrade to something better if you want sharp, in focus, photos with limited distortion.  the 75-300mm is cheap to buy, but you get what you pay for.  You can pick up a used super fast 70-200 f/4 L for  ~$500 or for the same money get a new EF 70-300mm IS USM.  If that is too much even the 55-250mm stopped down will give pretty good results. 

http://www.the-digital-picture.com/Reviews/Canon-EF-35mm-f-2.0-Lens-Review.aspx

http://www.the-digital-picture.com/Reviews/Canon-EF-70-300mm-f-4-5.6-IS-USM-Lens-Review.aspx