When Google Adsense recommend the 250 x 300 rectangle , it is realy honest

This post is after 1 month of variation and changes in Adsense placements, sizes and colors...
the over all notice is that the 300x250 rectangle which is recommended by Google is really the top CTR ad, the ads according to ctr are :
1- 300 x 250 rectangle
2- 336x300 rectangle
3- horizontal link units
4- 468x 60 banner
5- 768x90 leader board
6- others... vertical link units , square , button .... all the lowest

the best ctr according to colors :
(this I noticed a big variation from different countries, US and Europe visitors tend to click blended ads with no borders , same background as page, Middle east and others tend to click ads that are put on a very contrasted colors as a black back ground on a white page with yellow links !)

Best CTR according to placements
1- Header ... top of page best bellow title or H2 header tags
2- Inside content
3- Footer

After this trial I recommend very much every publisher to continuously change colors, placements and sizes of his ads until reach optimum ctr.