If Classic Sudoku can not satisfy you anymore, try the X-Sudoku Level Expert. -Each puzzle have 1,2,3,4,5,6,7,8,9 on the top.
It is for you when you clear one number, Bang it off This series have four different levels: ea.
Good luck X-Sudoku Expert Level vol.1 Details - Small Print (5x8) to easy take with - 100 Expert Level Sudoku Puzzles Collection - You can challenge yourself by writing down the time, you used.
You have new challenge for diagonal In Expert level, you have 21-23 known numbers.
If Classic Sudoku can not satisfy you anymore, try the X-Sudoku Level Expert