With the ever changing algos I dont thing anyone knows for sure the size of the pieces but we can all take a wild guess and each one of us will guess different.
For 3 years I could not put a web site in the top 100 and after I learned CSS the last 4 years I have put every site I optimize in the top 10. Valid code is just as easy to write as invalid code and it is just my preference to valadite every page through the w3c. It seems to work for me so I am happy.
Don
Seopro