You still haven't answered the question of what part of your throttle range you're trying to tune by messing with the needle.
Why would you want to use a dellorto needle in your mikuni? Your local motorcycle shop should have mikuni VM carb needles in stock.
If you're running lean at WOT, the answer is not changing your needle, it's changing your main jet. Main jet is the only carb part affecting mixture at WOT.